Or go to a real hardware store and just buy Masterlock locks keyed alike! They are in plain cardboard boxes of ten or twelve.
Both of my Pelican gun cases have two tabs for locks. Inside, in cutouts in the foam are two extra locks. On my Pelican ammo box is another lock and an extra inside. All these locks are keyed the same and I have an extra key inside my carry on, as well as my keyring. Wife has an extra also.
Come to think of it, my wife's Pelican carry-on size camera case has a keyed alike lock in it, although as carry-on, it isn't used much.
We do use TSA locks on "regular" luggage.
