Tyre sizes are either 245-45-19, or 255-45-19. My preference was for the 255s as they offered a smidge more protection to the protruding spokes.
There are a few sets of wheels for sale on ebay at the moment, but be prepared to travel if you have to for the right set. Most will still have Amarok size tyres on them. You may be able to sell these to recoup some money, but don't expect a lot.
@Skyliner33 was selling a set with tyres a while back, but don't know if they are still available.