There have been a number of posts on this subject. To buy new, there are 16" x 6" wheels sold for trailers that are a good fit. I used two of these on my 1951 1 Ton. I think that this site will give you the information:

http://www.lowcosttrailersupplies.com/trailer-parts-wheels.html

They are called OEM style wheels. If you don't mind the look, the spoked ones will do the job also.

There are some wheels from the 80s, GM, Ford and Dodge that are 8 lug and 16" x 6". The issue here is clearance at the front for the tie rod ends and clearance for the drums at the rear.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!