modern motors or national should have a few in stock. pretty common wheel.
where's your head at Eric? a 15x8" wheel won't fit on Chev/ford/Dodge 3/4 tonne so its probably not in the store. lots of options for those trucks just sitting in the showroom. 17/18/20" you know it. lots o' selection.
last time i was at either store, they didn't have any in stock. that was a while ago though. best bet is to drop by. there actually is a good chance modern will have some. or national.