I was just wondering if there are one piece rims for the 2.5 ton?
Thanks
First off welcome to SteelSoldiers. Nice to see another person join in on the green disease.

As far as your question about rims it all depends on what your plans are. Since this is your first and only post at the moment and you have yet to post an intro that tells us what truck(s) you have along with your plans for it/them it's kind of hard to give you a direct answer. So I will try to cover several possible routes and maybe one of them will answer what you want to know.
If you are looking for one piece 20 inch rims to use the stock NDT's on then the answer would be no.
If you are looking for a possible rim to upgrade to that is one piece yet will let you keep the dual tires on the rear for a near stock appearance then that would be the 22.5 rims that others have mentioned. Accuride sells a 22.5 rim that has the same number of holes in it as the current 20 inch rim. The down side is they cost something like $250 (according to another SS member from a thread a couple weeks ago about the 22.5 rims). If price is an issue check with some semi truck junk yards in your area as there are several civilian trucks that used them. But if you want a really stock looking appearance tire wise then you might not want 22.5's as no one makes NDT tires for them. If you don't mind a more civilian tread then take a look at the tread of the Goodyear G177's. I have some Wingfoot retreads on my semi truck with the same pattern and when we drove through the Canadian Rockies in a massive snow storm they worked great and I never had to chain up.
Last option is are you looking for a 20 inch rim that is wider then stock to use with larger and wider 20 inch tires like the 14.00x20 or 16.00x20? If so then no, there is no one piece 20 inch rim for those either. But if it's wider tires you want you can either go with 2 piece rims for the M35A3 or HEMTT 2 piece rims with an adaptor plate. While they're not a one piece the nice features with the 2 piece rims are that they bolt together (i.e. you can change a tire easier without any special tools and they don't have the potentially deadly split ring) and they have a rubber o-ring between the two halves so you don't need to use a tube with them.
Hope this helps. If not please let us know what kind of tire you want to be able to use and maybe some one can give you a better answer.
Ruppster