Summary

several chairs from Transformers as a franchise, including
-Ark seats(G1)
-Autobot Shuttle Seats(1986)
-Moon Base 1 Seats(1986)
-Blaster's comms chair, with a swiveling/removable keyboard(1986)
-Megatron's Throne(Armada)

none of these have a lot of detail, but they have the correct general shape. You can scale them up or down 20% or so for minibots or larger characters, but don't expect someone like Ultra Magnus to be able to sit down without a decent scale change. Just make sure to measure how wide and long the seat would need to be in order to seat who you want. The seats by default are anywhere from 50-60 millimeters in length and width, usually wider than they are long. I based the scale of the generic seats off of Earthrise Prowl, who should fit pretty well into them. Blaster's chair is based on the Legacy/SS86 mold, and Megatron's throne is an estimate, though it may not be wide enough for the Legacy figure to use.
I'm willing to tweak the proportions on Megatron's throne, if someone were to give me the measurements of the Legacy figure in a seated position at a rigid 90 degrees at each appropriate joint, in order to fit him neatly.