You can find Ford Window Lift assemblies at any Auto Wrecker. It doesn't matter if it is Left ,Right, or Tail gate! The Motors are all the same as are the gears.
As a matter of fact these exact same units were also used by G.M.and Chrysler , back in the 70/80 ,s! the Left ones just have the same shaped housings that Kwikee used.
Kwikee modified the housings to fit their particular application by grinding down some of the mounting studs ! You are really only after the Gears inside, and/or the Motor.
The exact same Motor and gearbox was also used for various Windshield Wiper applications as well!
And Yes You can still buy them New at NAPA and other Auto Supply Stores.