The following are early designs of mecha in Super Sentai from a concept art book released in 2002, so there isn't anything past Hurricanger.
Super Sentai Mecha Concept Art
Goranger and Dynaman - Varibuloon, Shuttle Base and Dyna Robo
Concepts for the flying fortress of the Goranger and the Giant Robo of the Dynaman.
Liveman - Live Boxer, Maskman - Great Five, Changeman - Change Robo and Flashman -Flash King
Live Boxer was the robo of Green Sai and Black Bison. It also showed different heads for Great Five.
Jetman - Jet Icarus, Jet Garuda, Fortress
Jetman had no Fortress but it looks like they were to have one.
Other Early Sketches
I am not sure which these were for, but I think the top one was for either Jetman or Maskman. I think the reason I think it is Maskman because of how the robo head looks. The reason I think it might be Jetman is because blue and pink look female. And it looks like it needed two other robos to become one full 'megazord.' The winged robo below looks like Jet Garuda. And the one to the right looks like Titan Boy with another robo and ship. And the one to the left looks like from Turboranger or another series.