What about the Aerosoft Twin Otter, it has tundra wheels, ski's, amphibian and it works in P3Dv4.5 with an decent autpilot and a lot of goodies. I Fly VR, and this is still a very fine aircraft. Maybe to big.
Recently the converted Maule from FS2004, but the cockpit need some work. Is has big tundra wheels.
Virtualcol has also a Otter, you get 2 planes in the package a normal Otter and a turbo Otter, with Amphibian, ski;s wheels and tundra.
Hope this helps.
Waviateur