Anyone know of a good mud tire for 16.5s.  I am looking for a less expensive tire about 33-12.50-16.5.
Any help would be appreciated.  

I have been using bias ply 9.50x 16.5 10 ply rated studded mud/snow tires for many years on my plow trucks. they are only 31 inches but they are really aggressive and fantastic in snow and ice and decent in mud. Nice thing about a bias ply tire is that they have a really tuff sidewall that you are not going to have a easy time damaging.  

I'm looking for a radial because my truck will be sitting most of the time and i don't want flat spots on the tires.  

They only flat spot when you park it with tires hot and it goes away when they warm up. I have been using them for years and I have no tire wear issues and I actually prefer them off road (bias ply) the radials because of tuff sidewalls the thick carcass makes lugs on edge of tires dig in better. Radial are better if you drive street a lot but off road you cannot beat the tuffness of a bias ply. I have seen many offroad radials fail due to sidewall damage but never had a bias ply fail.They used to make 16.5 in 10.0 and 12.0 in bias ply and might still be some made if you look around. A "10" would be about 32 and 12 about 34.