I would take one of the wheels you have now and take it to a salvage yard, scrap yard, and show them (might want a tape measure as well to double check the bolt spacing,) but show the salvage yard and see what they may have in larger rims with that bold pattern, and most likely would will come home with few usable rims for a $20 bill or under,
going larger should not be a problem going the other direction could be (larger to smaller), (once had two Chevy wheels one was for a all drum brakes pick up, and one newer with disk brakes on the front axel) simply said my son did not check the spare he was using and it hit some thing and nearly did not get the pickup off the road one night, needless to say he did not drive it home) but by going larger I doubt you would have that problem,
(he probably could have pulled the back wheel off and put on the front that was flat, and put the spair on the rear and it probably would have cleared, but did not think of that when it happened),