Is it possible? And does anyone know an online vendor that sells the part?
Henry - 15" 2.2 GHz MacBook Pro, OS X 10.4, iPod Mini
the keyboard should fit the older ones.
the keys are interchangeable with all ibook models (at least) so their thickness has not changed (only the opaqueness) so in theory you could use even use a clamshell ibook keys for replacement.
apple.com online store sells them, if i remember right for about 120 $ plus tax.
and you can get different layouts too (e.g. spanish, german etc).