Have you tried looking at http://store.nintendo.com ?
Where can I find extra parts for the balance board ?
I lost a removable pad on the bottom.
the pads are only needed for thick carpet.
so while you wait on replacements you may possibly get-by by placing the balance board on a 12"x20" wooden board -- between the carpet and balance board. (31cmx51cm)
this may be unsafe if it's any other size... but i doubt the balance board will skid off the wooden board...
You must good to take care it.
Mod Edit: Alternate links aren't allowed, sorry