You won't find an OEM battery for any Apple computer unless it is taken from another computer. Apple does not sell parts to their products, I would assume, because they want you to pay the costly markup of them fixing it for you.
I highly suggest giving the new one (it is stated to be up to OEM Specifications, otherwise just as good, if not better, than the original Apple part) on this website a try - I did, and it's working great. The repair process was rather tedious and lengthy, but worth it if you don't want to invest $2,300 or more on a new MacBook Pro. It was also for an A1398 Model, Early 2013 15" Retina.