I have a case of Winchester AA you can buy. These are the desirable gray hulls. I bought it from Cabelas earlier this year for a class but didn't get around to using this case.
Are you looking for local sources or somewhere to order online? I do bidness with www.ammunitiontogo.com . Their prices aren't the cheapest but they're not really out of line either. Shipping is usually nominal based on weight (which is a consideration with shotgun shells). They've got a great selection of 'specialty' rounds also.