if you find one, you might wanna pull a lot of electronics and give it a dry run before you drill a hole in your tailgate. I think if you just hook up 12 volts to that thing, it'll go real fast and probably break something.
That gets me thinking...did you say you were mounting it in fiberglass? That might be the reason they didn't offer one...you might want to reinforce it big time before you let ol' Toyody torque on it