As to the Tundra towing mirrors....
check Sparks Toyota TRD in the Carolina at TRD Toyota-Scion Performance Parts Accessories from Sparks Toyota-Scion
Their internet price on the mirrors currently is $199.27
as to the wiring, even if you had only the three wire, my Toyota service writer told me a week ago that the mirrors would work, but that the heater/directional light function would not work but the auto adjust would work.
someone on one of the Tundra forums had questioned whether the truck would pass inspection if the directionals on the mirrors didn't work.... the dealership said that wouldn't be an issue as the mirror directionals are a convenience add on, not a requirement.
so if the bolt pattern is the same you should be able to upgrade.