I've got a similar problem. I have a Pismo PowerBook G3 missing an option key and a dual USB ibook missing a delete key. After much research I discovered that you have to get a WHOLE new keyboard. You can't just get the keys you need. Although, that would be very nice and easy if it were the case.
If anyone does come across a place that sells just keys please remember this place and post it.
Thanks,
Brian