tractor tires

[dman10]

Hey ya'll,
I've been on a tractor bug lately, probably cause I've been restoring a 1:1 1958 ford 901 powermaster. But, I kinda want to build a larger scale (1/10-1/8ish) John Deere 4020.
If your not familiar:

And I have a few questions:
Tires, I don't know where to get large scale tires and rims. Any clues?
Powering it. I want plenty of power, for not alot of money. I would like it to be powerful enough to run a scale shredder and pull a blade if I can.
Thanks in advance,
"D"