Note for anyone who finds this thread in search of this part: there are several web retailers that try selling this part for $20-30 with shipping on top of that. You don't have to buy from them because Nikon is still officially selling these at $14 with $4 shipping (even with 8.25% CA tax it comes out to less than resellers)
But if you want to buy the overpriced ones, google for 'nikon 990 replacement parts'
(oddly, using words "coolpix" or "spare" doesn't have any results)
Thanks guys for this very useful post - my replacement battery compartment is in the mail