WANTED. 15" sbp steelies

I'm thinking that you meant to say wheel adapters that go from a 4" to 4.5" bolt circle as opposed to a spacer? If so, could you possibly get your current wheels re-done to have the offset changed? I have never really looked too close at cop rims because they don't interest me, but I can't see why it wouldn't work.........keeps the tires, your rims still match, no changing of brakes,it's probably not as a expensive as you think,and you can probably get back on the road quicker.........
15" with a 4" BC ordinary steel wheels do exist (I have a set), but I suspect they were not factory and are scarcer than hens teeth.........
Like others have pointed out though, 15" wheels with a 4" BC do exist and that may be the safer way to go. Not a real fan of adapters (or spacers). I don't think they are as safe as they could be.