This same keyboard is rebranded by about 20 different companies. No idea who the original is (Rii?). Also known as the Rii Mini, SiTouch Mini, and many others. Available in BT and RF (w/ USB receiver) flavors and available from a bunch of different websites; shop around prices vary greatly.

I had this crazy idea:

(that's an Atrix in the mock-up)

I'm guessing the OP wants to use the N900 in tv-out mode and control it with a wireless keyboard.