well...they definately make Cordura in brown. I'm not sure if ballistics nylon is the exact same as Cordura but it seems to me it would be similar. I've seen it on ebay.

I was looking for weapons cases quite a long time ago for my bo and shinai and found a website called Bujin Design
If they can come up with sources for the fabric here in North America I'm sure Stillwater can too.

back to the topic at hand I'm not sure I'd want to paint a a new sporran, but I'm wondering if you could give it a try on an old backpack or gymbag made of similar material?