Are there solar powered bicycles for sale in the US?

Depends on what you mean.

Making a bike that runs DIRECTLY off solar power is tricky. There aren’t many flat surfaces at a good angle to the sun on a bike. It’s difficult to get a big enough area to collect enough power.

OTOH, you can buy a perfectly normal ebike, and one way or another, charge the battery off solar power.

One option is to use a small off-grid setup, with panels, inverters and deep storage batteries etc. That’d allow you to use the charger supplied with the ebike.

Or it might be possible to find a solar powered charger that’s compatible with the battery of the ebike.