(denim) battle jackets for dummies
Everybody sells ‘em. You’re probably going to end up finding way too many pins than not enough, in fact, but if you’re really lost, places like Etsy, local record shops, thrift stores, and online distros are all good places to start.

Unfortunately I don’t have any direct experience in making pins, but you can paint bottle caps and superglue safety pins onto them to make your own. There’s also other methods, like using Shrinky Dinks, and you can see a tutorial for that here.

If your pins have a safety pin-style back, I suggest sewing them onto your jacket via the loop in the pin back to keep them attached, especially since these kinds have a habit of falling out.

If it’s a pin with a straight back (i.e., the back of the pin just has a little spike sticking out), locking pin backs are a wise investment. These can be found online or at some craft stores.

In both cases, sewing a small piece of fabric over the back of the pin can also help with keeping the pin in place, as it stops the back from being tugged on.