If you need a weapon of any kind, Crazy Joe sells it. From ancient weaponry to the highest of high tech, Crazy Joe will sell you small arms for a reasonable price. But if you can't make the payment, then you either have two choices.
One: You work off the debt in his store, probably learning about weapons in the process.
Or Two: You contribute to Joe's gray matter Picasso Collection on his wall. It doesn't look like dried blood for no reason.
The subtitle on the store says: "Come here for bullets and blades! Otherwise, GTFO!"