Where can I purchase an oem battery for MacBook Pro ?

I have a 2009 MacBook Pro that requires a battery model A1321. I'm trying to locate somewhere to purchase an original battery. For some reason this seems to be hard to find. Apparently Apple will only do a repair of the computer, but won't sell a battery. Most places I have seen online aren't really specific about whether the batteries are oem. It's impossible to tell on eBay as well. Can anyone recommend a specific store that will sell this specific battery? I've seen people recommend Lacomputer.com - but they don't list that model. Buy.com sells a battery but as far as I can tell it's not a real Apple battery. I'd appreciate any help with this - but I'm looking for a place that definitely carries the A1321 battery. Thanks.