People list what albums they have and you can find those people by clicking on an album. Have you ever contacted those people about having copies available? It does seem out of place to ask, but it seems like it would be a real convenient system.

VGMdb has a Marketplace (http://vgmdb.net/db/marketplace.php?do=view) and some of the users even have set up "For Sale" folders which one can easily spot on the same page you mentioned, or made threads in the forum to advertise what's up for sale from their collection(s).
So, yeah, a convenient system is already in place over there. Just make sure you choose wisely when asking if there would be interest in selling something.