Your plight is similar to a friend of mine that is trying to have "too scale" display of each character, he goes as far to use some other toys to represent OTHER characters like Botcon 2005 Virulent Clones as G1 Pretender Bugly and so on.
He had the same problem with Jazz and is hunting a cheap Botcon 2008 Mirrorverse one now. The movie ones won't cut it for him, neither will the original G1 toy. Also the action master, Spychanger repaint, pretender mini robot and any pvc are too small. Also the planned Legends Universe Jazz is also going to be too small...... hrrrmmmm..... so right now your stuck at the moment.
Get the Classics 2-pack with Prime vs. Megatron (Plus DVD) for your Megatron in green tank Megatron goodness in a nice size. (by the by Armada Megatron was an Ultra).
What no Hot Rod?