I don't know if this is pertinent but the Dutch Goalkeeper [naval] CIWS, in use from the early 1980s and still fitted to a couple of Dutch and British warships, uses the same GAU-8 multibarrel canon as the A-10 does. I don't think the Goalkeeper uses the special depleted uranium AP rounds, though- I'm not sure but I think it uses some form HE. Therefore, the ammo for the A-10 might not be as rare as you think.
http://en.wikipedia.org/wiki/Goalkeeper_CIWS