The only Bumpy covers I've seen are wool... somehow I don't think that's what you're looking for.
I hate to be the bearer of bad news, but I have to say, chances are you're only going to find the good stuff online. All the good sewing stores around my place are quilting stores and the general 'all purpose' type stores don't carry any of the really good quality stuff (Malden Mills fleece, PUL, etc, etc.) You can usually find a cheaper microfleece or suedecloth which will work but not the cover stuff.
When you buy from someone catering to diaper making you know that you're getting something that will work. After a few 'failed' attempts, I decided that it was best just to shell out a bit and get what I needed online. The results have been much better. I'm less frustrated and the diapers I make from my materials perform much better.
