With any hides that are store bought (as in a pet store) be sure to sterilize the hell out of it. Even those plastic ExoTerra hides should be sprayed down with sanitizer such as chlorhexidine at the very least. Anything organic (like the various things made from coconuts) should be boiled and baked.
I order hides from Reptile Basics. For balls I like that the opening is smaller, which will help them feel more secure.