You can get all Kyosho parts from kyoshoamerica.com
They became the main distributor of their products when contract with great planes wasn't renewed.
IMO, Kyosho and Mugen are the best choices. Serpent is a good car, but to be competittive with a good driver running one of the other cars is to be a better driver than him or you will need to upgrade the Serpent with several upgrades that Serpent has developed to make car comparable to the other two. Also, parts for the Serpent are more expensive since most parts come individually wrapped a.e. one knuckle for the left, another package for a right side knuckle, and so on.
Originally Posted by icon
Available 1/8th kits are dominated by mostly the big three in the US; Mugen, Kyosho, and Serpent.
Delta supports basically a repackaged Kyosho Evolva with their own mix of parts.
HPI discontinued the proceed, and parts are almost impossible to get. I personally own and love the proceed, but I dont recommend anyone getting one since HPI refuses parts support.
Motonica is relatively new. Interesting design concepts, but parts are expensive and not very common here.
If you are going to race, your best bet is the Mugen or Serpent. I have a hard time finding Kyosho stuff ever since they parted ways with Great Planes/Towerhobbies. Mugen and Serpent are much easier to get parts and support for.