I get quite a few of mine from Scalecars.com, but I really DON"T recommend it if you're looking for cheap ones. The prices are incredibly high reaching the $500 limit on some.So Scalecars is very good and VERY detailed with little things (pedals, gear knobs, interior matching the real thing, wood with leather, etc.)
but very expensive. Don't expect and McLarens, Lamborghinis, Ferraris, or late 80's Le Mans Porsches to come cheap.