Are you looking for aftermarkt rims that match the offset from the factory rims? I had the wrong figures before, it's around +55 and not +38 (for 15" stock, I just measured it), so I've edited this post. Aftermarket rims have different designs than the stock one, so the offset will vary. Also aftermarket rims are not made just for Honda Fits, they have to accommodate a wide range of cars that have different suspension geometries and wheel well spaces. But from my own experience, and from what some Fit owners are reporting, around +42 to +45 there aren't rubbing problems. One owner with a +42 offset and lowered suspension has said he doesn't have rubbing or bottoming issues. Here's a link that may help you understand (it helped me) understand better offset and other terminology:
http://www.rsracing.com/tech-wheel.html