There are some decent, although wider, v-treaded monster truck tires, readily available, inside the USA that may work for you. They are designed to fit on a standard 2.2 sized rim. Traxxas and HPI both have a good looking tire in this size. If you were feeling ambitious, you could probably narrow these tires up to make them more scale, although some of the bigger articulated 4x4 tractors do run some rather wide singles like these, instead of duals. In North America, narrower duals are more common, but there are some tractors fitted with wide floatation tires as well. Think forestry sized. Narrowing up a set of tires is something I have never tried, but the rock crawler guys do it all the time. Doesn't seem like it's to hard to do. You cut the tire in half and remove some width from it, then glue it back together.
Here are the HPI tires -
http://www3.towerhobbies.com/cgi-bin...P?I=LXPZV5&P=8
And here are the Traxxas tires -
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJK61
I bought a set of each of these tires. I like both, but the HPI tires are slightly taller then the Traxxas tires. Scale-wise, Traxxas tires have no writing on the sidewall, which is kind of nice. HPI has some molded on Mud King lettering, which may or may not bother you. Both of these tires are a good size for tractors in 1/16 scale. I favor the HPI tires a little more because of the extra height, and because they are slightly softer.