3M use to make a paint that was textured like suede. It was used in telescopes and rifle scopes. They discontinued it in the 80's, but a German company called Mankiewicz-Coatings LLC still makes it. They appeared to have a processing plant around NC, but I couldn't locate a supplier.
Other alternatives are to apply felt or velvet to the walls. JoAnne's fabric sells rolls of velvet. Duvetyn is suppose to be better than velvet at absorbing light, although most prices I've seen were too much to do a whole room.
www.rosebrand.com sells theatrical equipment including a plethora of masking fabrics, paints, and professional theater draping systems. Check out the online catalog, the website itself is fairly bland.
A 3rd possibility is to use Flocked Paper. It's paper with a layer of black peach fuzz bonded to it. You can even get it with self adhesive backing. It's used for telescopes. Edmund Scientific sells is, but for room size quantities you're much better off going for bulk discounts. It's fairly common and you shouldn't have any problems finding it.
The aerospace and supporting industries also make specialty black paints, but they're geared (and priced) more for painting your Stealth Fighter than your home theater.