Does anyone know of a source for plain (i.e. non-rally and non-"smoothie"

15X8 GM steel wheels with a 4.75"-5" backspacing? The closest thing I've found is by Wheel Vintiques but the appropriate size/backspacing is only available in various Rally forms. [img]<<GRAEMLIN_URL>>/dunno.gif[/img]
If this fails, any recommendations where to go for widening and altering an OEM rim to spec?