I have found that for 84-87 Fieros, most anything (within reason) that will fit on a Volkswagen New Beetle will also fit on a Fiero.
The sizes and offsets (~35mm) are just about perfect. Bolt pattern and center bore (57.1mm) are identical.
For the front of an 88, you will want something with a little more offset (~40-48mm). I usually base my search on a Subaru Impreza. The only real "gotcha" is that stock Subaru wheels use a 56.1mm centerbore. Aftermarket wheels, unless they are Subaru specific, usually are "70-something" mm and use hub-centric rings, so that shouldn't be an issue.