There used to be a guy that made them and sold them. I remember watching this years ago, no idea what the site was... I remember he had a youtube channel where he showed off his portable N64, GC, SNES, PSX, etc... and linkied in the description to his site, where you could make your orders. It's probably still up.
I didn't get one because they were way too expensive, and it really felt like a hassle after you get over the cool idea bit (they are huge, so barely portable, and they suck up batteries real quick).