I hate to be the bringer of bad news, but this car is discontinued.
I spoke with Mugen directly and they flat out told me they no longer support this car.
Getting parts is next to impossible. Unless you have deep pockets, know someone that works at a machine shop and can make parts for you, (a la Carbon fiber or aluminum) Its best you cut your loses and move on toward an HPI RS4 evo.
I've seen a few used MSX's on craigs list but as far as key parts like shock towers and arms forget it I've scoured Flee bay but olny came up with insignificant parts like the bumper, body post or radio tray....alll the things I could have easily gotten anywhere.
I got lucky and sold mine to a guy who wanted a beginner car for his son. I told him getting parts will be impossible. He still wanted it. I gave it to him for $70 bucks.
Should you be lucky and find an old hobby shop in a corner of the world somewhere, be sure to get a few rear shocktowers. Those things were notorious for snapping like twiggs on a cold winter night.
Ofna has/had a car that looked similar to the Mugen car. I thought they stole the design form Mugen when I saw it. Their front shock tower may work on it. As a last resort, check there. Towere Hobbies may still have some parts for the Ofna car.