Some arcade auctions (such as the Indianapolis one by US Amusement) have a box of locks on the checkout table, and they'll take a bulk offer on the whole box. That's where a friend and I got all of our locks at a very reasonable price.
On cabinets with tons of locks (like some Candies), I'm a fan of keying the coin door, and possibly the coin bin, if you actually use it for anything, alike, but then using spare locks for the rest, ideally also keyed alike, even if different from your main key, and hanging the key inside the coin door. Often, there's a spot to hang keys there, anyway, as that's usually where the key for the back of the cabinet gets hung.