I took my sporrans down to Walmart, and matched them up to the regular dress belts. You might have to go to the women's belt section to find one to fit your sporran. That is if you don't want to make the strap yourself.

The other thing is to get a couple of chain dog collars, they have welded and polished links, and use those linked together if you want the chain. Guess the casual would be more with the leather belt for a strap, though.