kings motorsports is the only authorized stateside dealer for Mugen. I also know one other guy, but be prepared for a super long wait of 6-8 weeks for delivery and major $$$ for the part and shipping.

http://value-caraudio.com/

Email him and tell him Mr Hyde sent you. So far I got my rims, Inspire door sills, Mugen Pedals, and a bunch of stuff through him.