There are options, but probably more so with used Class B's than new. Our 2005 Leisure Travel Vans Free Spirit 210B 3S model easily sleeps three (hence the 3S in the model number) but finding one used would be a real issue.
The 3rd seat in front is probably the most useful of those in Class B's with an extra bed up front. I have slept on it for 6-week trips twice when I took two different sets of teenage grandsons to Alaska. They slept in the back on the main bed and I slept in front.
And related to Class B space, it's certainly doable with three but not everyone would probably find it their thing. In our view the space trade off is good one for the increased maneuverability.