Let me add a few words from the other side. Radials do not always improve handling on the older trucks. They can make the rear end of the truck move around, especially on the highway. The also are a lot harder to steer, due to the increased load path of the tire. If you don't usually exceed 60 mph, you should be happy with bias-plys on your truck.
As was said, locate a good dealer in your area. Usually one that does a lot of commercial truck work will be able to help you. I'm running 7.00-15 8 plys on the front of my 52 3/4 ton, my dealer has them in stock, they're made in Mexico.
