Here are the 15" wide variety but also available in 15x6. The 4 nubs would be great in case you update to disc brakes later. The 16" from the 71, 72 Blazers I think are 16x5 and require more searching.
Links shown just for reference.
Look at this on eBay:
http://www.ebay.com/ulk/itm/281929518866
67-72 73-87 60's 70's80's 15x8 4x4 6 Lug Chevrolet Truck K5 Blazer Steel Wheels
http://www.ebay.com/ulk/itm/141836918294
6 LUG STEEL 16". For drum brakes