Если о стандартной карусели (по 1 слайду), но именно с карточками, то вместо картинки вставляете карточку:
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/css/bootstrap.min.css" >
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/js/bootstrap.min.js"></script>
<div id="carouselExampleControls" class="carousel slide" data-ride="carousel">
<div class="carousel-inner">
<div class="carousel-item active">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="carousel-item">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="carousel-item">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
</div>
<a class="carousel-control-prev" href="#carouselExampleControls" role="button" data-slide="prev">
<span class="carousel-control-prev-icon" aria-hidden="true"></span>
<span class="sr-only">Previous</span>
</a>
<a class="carousel-control-next" href="#carouselExampleControls" role="button" data-slide="next">
<span class="carousel-control-next-icon" aria-hidden="true"></span>
<span class="sr-only">Next</span>
</a>
</div>
пример 1
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Если же Вы хотите прокрутку по 3 блока, то стандартное решение .row и .col-4:
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/css/bootstrap.min.css" >
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/js/bootstrap.min.js"></script>
<div id="carouselExampleControls" class="carousel slide" data-ride="carousel">
<div class="carousel-inner">
<div class="carousel-item active">
<div class="row">
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
</div>
</div>
<div class="carousel-item">
<div class="row">
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
</div>
</div>
<div class="carousel-item">
<div class="row">
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-4">
<div class="card">
<img class="card-img-top" src="https://dummyimage.com/286x180/ccc/fff" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">Some quick example text to build on the card title and make up the bulk of the card's content.</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
</div>
</div>
</div>
<a class="carousel-control-prev" href="#carouselExampleControls" role="button" data-slide="prev">
<span class="carousel-control-prev-icon" aria-hidden="true"></span>
<span class="sr-only">Previous</span>
</a>
<a class="carousel-control-next" href="#carouselExampleControls" role="button" data-slide="next">
<span class="carousel-control-next-icon" aria-hidden="true"></span>
<span class="sr-only">Next</span>
</a>
</div>
пример 2
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И вот еще на codepen готовые решения есть