I have NO idea what I'm looking at in that picture.
If it's just part of a normal cam lock, like the ones used to close an arcade coin door, then you need to ask the Lowe's guys for "Mailbox Locks". I'm guessing it's not that, though, I'd suggest digging around in their random parts aisle (usually near the nuts and bolts, they have all sorts of unusual connectors and cabinet bits and pieces).