there are several ways you can try to get it out. First you could get an easy out screw extractor from sears, or you can jb weld an old allen wrench into the stripped screw, let it dry completely, then remove the screw.
Those screws are 2.6 mm, make sure you get the exact replacement from OS, or Kyosho makes a 2.6 assortment. Don't try to use 2.5mm screws.