I thought of a way to convert a Thunder Lizard (or maybe just a baby one).
First, you take a Stegadon (or two) and bulk it up somehow (maybe just put extra armor plates from the second Stegadon on it). Then, you take the neck and tail from either Prince Imriks High Elf Dragon, or the neck and tail from a plastic High Elf Dragon kit. Next, put the three pieces together and use the un-crested Stegadon head as the head after you sculpt scales onto the flat parts. Finally, mount it on a Screaming Bell Base and enjoy! It should look like a Brachiosaurus-ish dinosaur.
Cheers,
Chaq Mundi.