I know the rules for autocross changed quite a bit since I did it, and your sanctioning my be different...

When I was running autocross the rim width wasn't as important as tire width... you could run a slightly wider rim with a stock width tire and still fall into the same category in most classes.. Which class are you running it?

I "think" the rims that will fit the aveo in 15" rim that is 5.5 are off a mini cooper. i forget the center bore of a mini copper. I think the aveo is 56.6, I know a honda is 56.1 and vw is 57.1. Centerbore is important. The honda, kia, and yaris all have a 4x100 15x5.5 rim, but you will need to heck offset and centerbore.