searching is not easy. Too many variants on the name: audio grills,speaker grills,audio screens,speaker fabric... everybody calls it something different. Fabric selectionis at acousticalsolutions.com/products/fabrics/grille_cloth.asp but i doubt you can paint on it. I did find a...
Check out decorative bamboo. Large diameter bamboo is decorative and easy to work into the room decore, yet it's hollow and can be drilled for entrance/exits. The inner walls of large bamboo canbe very tough, but my buddy showed me a trick. A steel poker (used to break up concrete and stuff)...
I'm doing the same, looking for custom audio screens. I found masquerade-speakers.com. Artcoustics is way too "sophisticated" for me. (Sorry no URLs... it didn't allow me since I just started) Any others?