I know two places where you can buy keypads but I don't know if they are trustworthy:

- ecase shop
link : http://www.ecaseshop.com/replacement...ck-p-3671.html

$ 8.99 is the price and they also sell housing and cover,beware I don't know if they are good....as soon as I get a n900 I'm going to buy some stuff from them.

-the nokia parts
http://www.thenokiaparts.com/eng/tuo...00-spare-parts

€ 14.00 is the price,they look good but atm is out of stock.

These are the only websites I know for n900 spareparts', if I find something else I post here.

edit

check also these guys : http://www.blueunplugged.com/Origina...ad-QWERTZ.aspx

looks safe because is in the UK.