Testor's did carry a line of Nascar colors back in 1998, but had to stop due to a little thing called copyright infringement. They did not want to pay the very high licensing fees so that line was discontinued. Much the same way Slixx decals stopped producing their excellent Nascar decals because of the fees.
As for the 48 car, I think Model Master artic blue looks like a close match. You may want to check out Model Car World or Slixx Decals. They both carry a line of paints for racing that is an exact match to the real thing. The paint costs more but at least it's the right color.
Darren