You can check the online gun auction sites or might get lucky w/some used mag's at gunshows. I've never found any deals for new mag's anywhere, tho. I've now got 7 fully functional mag's for my XD-40, so stopped looking.
I haven't found any breaks on XD45 mags. I don't think mecgar has made knockoffs yet.
Yupp was about to post that same thing.
MecGar makes GREAT aftermarket mags particularly for the 1911's but they havent dont XD mags yet. Might just have to suck it up and go through the Springfield site or other retailers.