I would try Excalibur Motorsports
www.atv4usa.com as they distribute a small but decent-quality lineup of product, including the exclusive distributor for the TMEC 200 enduro. I have been there in person and sat down with the owner Wade Liu, and the head manager Alan Tang. They are good with parts, or at least any parts I have needed for my TMEC 200.
I would also contact the company, SSR Motorsports as they have a wide range of quality scooters and bikes.
Not familiar with Extreme.