I'll second the mention of BigSkyCaseCovers. I purchased one based on the recommendation of someone on this site a few months ago (might have been "Bob_k," but whoever it was I appreciate the recommend).
My Americase is slightly "angular" and I didn't think a standard Americase cover would fit correctly and I wasn't really interested in the velcro atttachment marring the case itself.
The case cover I received from BigSky is perfect. The Cordura is a heavier weight than that on my other, standard Americase cover, by two to three times. Jim Foley, the owner, was very nice to work with since I had to make slightly special arrangements for delivery.
The price is greater than that from Americase, but you will be getting a much better product, custom made in Missoula, MT.
I don't think you'll be disappointed if you choose a BigSkyCaseCover.