I'm not sure of web sites but I've had dirt bikes for years and the popular tuners can be found in the motoX magazines. The big players are Race Tech (suspension) Pro Circuit (suspension & motor mods), FMF (motor mods, pipes, I think they've started suspension work). Acerbis and UFO are the big players for body work. I have to give my brother in law a plug, he owns jdjetting.com. He's a jetting guru. He's mainly into 4 strokes but I think he has some 2 stroke jetting kits ( I've seen some 2 stroke CRs and YZs in the garage).