They are EXTREMELY rare. Last time they were up on Ebay in 2009, they were listed at $15,000 (for the whole set.) Not sure if they actually sold at that price, but that gives you a rough idea of the pricepoint for these.
Your best bet is probably to try to buy a G1 Groove (or even a KO G1 Groove) and repaint it. Kryon Fusion for plastic is a great spray paint for Transformers as it bonds nicely to the plastic.