Pretty much what Jlee said, they are everywhere, and you can find them cheap as Heck. As for with the clips on, you might be able to find them on ebay or something, but tbh its not that big of a deal. Normally, I'm against using electrical tape for save battery replacements and suggest buying a pack of battery holders along with the batteries. However, when it comes to Gameboy carts, tape is the way to go, just because the pressure should keep the battery in place much easier than say with a SNES cart and most battery holders won't fit in GB carts.