http://www.actionsalvage.com/truckbeds.asp They offer fiberglass replacement Long Bed units for 1984 - 1988 Toyota pickups, and short bed units for 1979 - 1993 (?) pickups.
... And then there's B&G Fiberglass, which offers replacement fiberglass beds for 1984 - 1995 Toyota pickups. http://www.bgfiberglassusa.com/index.html