They don't sell the part but they repair it for you here.
If you don't have the 3G model, I honestly don't think its even worth it.
EDIT: What I can think of is buying a broken as-is kindle off of ebay (With a working display) then use that and switch em. Here are some that look like they'd be up for a frankenstein-ing
I ordered one for my cracked kindle 3 screen, thanks to the guides on youtube the replacement was not very hard, took around half an hour, now my kinlde working like new again.