In "default.ide" u can find:
# Id, Model name, Txd name, Type HandlingId Game name, Anims Class Frq flags Comprules
401, bravura, bravura, car, BRAVURA, BRAVURA, null, poorfamily, 10, 0, 0, -1, 0.72, 0.72, 0
By changing the parameter "frq" frequency i believe u can make those cars apear more times...
also...
in "cargrp.dat" u can add "euros" in all lines, just to make sure it will apear in more places, because it will.