15" X 6" with the correct bolt pattern are often found on older 3/4T and 1T ford vans. When looking, stay 1997 and earlier as 1998 was a change year.
Just a note here, There are 2 common bolt patterns for 8 lug wheels, 8 on 6 1/2" (160mm) and 8 on ??? (170mm.) The 170mm wheels started in 1998 and by 2003 all 8 lug factory wheels were 170mm. Ford wheels are all over the place in diameter, with 16.5 being the most common, 15" next and 16" the hardest to find. With Dodge, 16" is the most common I've found, with a smattering of the others. Chevy common sizes are 16" and 16.5 and it seems rare to find any thing else. All stock offsets seem to be 3 1/2" to 4 1/2" no matter whose wheel it is, except for some Dodge "mudders" I saw. The center hole size is all over, too. Most of the 8 lug (Chevy 3/4T) wheels I have seen seem to be lug centric so it doesn't matter as long as they fit. I'm in Raleigh NC, so all this applies to areas about 100 miles from home or less. Your mileage may vary!
best wishes,
Les
