Where Can I Still Find a Battery for the iPod Mini?

I've already had to replace the battery on my iPod Mini once. Even back then, it was difficult to find one and I ended up with a battery that was really for a newer iPod Mini and was not a perfect fit. However, with some modifications to the insides of the iPod, that battery fit and worked for over a year.

Now that replacement battery has died. My iPod will fit either the original iPod Mini battery or the newer Mini battery now (they don't make the Mini anymore I guess, so by "newer" I still mean black and white, old fashioned iPod). Any ideas where to buy one?

I keep thinking about buying a newer iPod, but really I like the black and white better because it is easier for me to see. So I think I'll stick with this one for as long as I can.