Couple ways you can go, you can look for originals which are pretty rare and are lock ring wheels or you can do like I did buy wheels from a later model Ford or Chev in 8-lug style mine are from a 1991 3/4-ton Suburban. The thing to also remember is if you are running the original tie-rod you will have clearance issues due to offset with modern wheels. I added clips to mine so I can run original caps and I modified my front end for clearance, here is a picture of them installed.
http://community.webshots.com/photo/2714049360102454676KZVSpY