The Kala Brand Music Co. has them on their web site, but there doesn’t seem to be any way to buy it from them. There are no buttons to add one to a cart.
Your best bet for getting a uBass is going to Road Toad Music. They have both fretted and fretless models in stock on their site.
Or you could try eBay. There are usually five or six available new there. There aren’t any used ones on the market yet (at least on eBay anyway) either because they are too new, or they are so completely awesome that anyone who has one does not want to part with it.