That's a nice deal. If you stare at battery cases on aliexpress.com, you can probably find some chinese seller selling it. Ypu can often find parts for the popular stuff. Otherwise, you could google back to the biker seller, probably a Canadian outfit?
Worst case, you re-wire the power thru one ot the undamaged pins. They probably use only tow of the four. but the only way to tell is to look on the back of the pins.
What I have done on a battery with a broken connector is to bring out the power thru a cable. Do the same on the bicycle side, and use a power connector,