camaro with 16" 85-92 used them due to the fact they couldnt be had with disc brake rears like on the TA , i had a pair of an 86 iroc but only found one when i went looking
they were steel from gm and the holes fit the lug studs closer than store brand spacers
almost any parts store should have thin spacers , my local parts store in town has them , and they arent expensive ,
One more option. I picked up my spacers from a guy in California. He is a retired Drag Racer from the 70's / 80's. I can't find his website right now (very cool pics as I recall of his cars from back then), but kept his phone number. If he is still in business, give him a call.
Fred Goeske - 818-992-5700.
He has a CNC machine and will custom make variable width aluminum spacers for any wheel, any bolt pattern. Not a cheap solution, but quality stuff and if you know exactly how far out you want to go (by wheel) he can do it.
My rear is not centered to the car, so I actually needed two different spacers for just the rear. I have since found this is not that uncommon on the G-Body's..