Doug,
Here's two additional options for you.
1) Buy a set from one of several wheel vendors (i.e. Wheel Vintiques or even closer ... Stockton Wheel (which is located right in between our locations). They basically take OEM centers and weld them into bigger/wider hoops.
2) If you do come across any 15x8s (with OEM backspacing), you can do what the companies above do and have someone cut the centers out and re-weld them to where you need them to be.
Good luck.