There is the Pacific Reach IF. 451 wheels and can be rolled while folded. It's discontinued but you can find the occasional bike crop up on Craigslist and you can still buy direct from Pacific Cycles. They have very limited stock but if you contact them through their website, Max Yeh will work with you. The frame does fold but that secondary bar does provide additional support and rigidity to the frame.
Here's a link to a review by the defunct NYCeWheels. (I do miss their reviews).

The Birdy's can be rolled when folded. Video of it here:

It also has a rear rack designed for it that has roller wheels that allow you to roll it when folded. There are also lots of after market roller wheels that you can install without a rack to roll it. If you want 20" wheels, you are looking at the Birdy R 20. It's difficult to find Birdy's in America. You may want to work with Bfold in NYC or directly with Pacific Cycles. That or take a vacation to Asia where you can find good deals on them and pack it into your suitcase. (Once travel is safe again).