Diamond: 15" rims - How much offset/backspace?

Diamond,

I am after a bit of information on what the common backspace/offset measurements are for 15X7 or 15X8, 5 on 5.5 inch white spoked steel wheels. The stud pattern is commonly found on Suzuki, Jeep, and Ford F100 rims.

I am hoping to go with 15X7 with about +12mm to +18 mm ("domed") with 31X9.5R15 Simex Centipedes , and need to know if I need to have the rims made up, or I can buy them off the shelf, and what manufacturer etc.. I have had lots of conflicting advice from various tyre stores ("They don't make them for Kias", "We don't have them in stock but we can get them in...", etc.), whan all I was after was information. Looked on the various sites (CSA, Sunrasia, Speedie, ROH) and they arent all that helpful either.