measure the offset!

see how far from max inner limit to max outer limmit and see where the wheel mounting face is in relation to them.
Figure out a good sized rim for a 215 and then figure out the offset from there!

http://www.rsracing.com/tech-wheel.html

To find a rim with that offset i would assume you would have to goto a 2nd hand rim dealer and go measure the backspace off all his rims in the size you specified. Or see what offsets you need for a 5.5", 6" & 7" rim