Since the Nats lost Syracuse when the Mets bought the franchise, could the Nats buy another IL franchise? Rochester or Buffalo? How about Charlotte, which was the Old Senators' (Griffith) A franchise? They are a White Sox franchise now.
Not sure how accurate this site is, but...
http://www.thesportsadvisorygroup.com/teams-for-sale/Someone pointed out a while back in another thread that the most logical move may be to buy a share of an existing AAA, as there doesn't appear to be any currently for sale.