Ask in the stores - I was given one but tried everywhere to get a second for a mate, but no luck. To be honest they are too small anyway for a nav flight as they are too small for a plog and useless if you are in the circuit as they get in the way.
KneeBoard with Eyelets & Clipboard
These USAF ones are ok
Pilots Flightboards
A non folding kneeboard is best for nav as they can be placed alongside your leg out of the way. This is big enough for a detailed plog and charts, with slots behind for rules and a douglas ptr.