you're unlikely to find much in the way of niche online-futniture stores. I've seen them very rarely online, all were custom-builds, and all the ones I remember seeing were descriptions of prior designs and orders on someone's web page, not items for sale.
You'll have the best luck contacting someone in your area (or within pickup-distance) that does custom furniture design.
There is one site that I know of that makes ABDL furniture and that's Baby Apparels. Their costs run pretty high, but the products look decently made, I have never actually tried any of their furniture though:
If you are looking for cribs, one of the users on the site, Ungulate, makes and sells modular cribs online. I have never tried them, but they seem like a reasonable alternative to full-fledged AB cribs and you can stow them away after use to prevent being found out:
Lastly, echoing Bambinod, lots of AB's either seek custom jobs or they try to make their furniture themselves by converting large pieces of furniture like dressers into changing tables, making an adult crib out of 2 baby cribs, that sort of thing. So, bottom line, you have a few options open to you