Dinoraul makes some excellent dinosaur models.

http://www.renderosity.com/mod/bcs/?vendor=Dinoraul

There even a t-rex there with an extended license.

The thing about creature modeling is that there are a few specialized vendors who really target that market and produce very nice products. It's a very niche market and they've already got it fairly well covered. The exception might be with certain one-off sorts of models that come out of the blue and don't have a specific type of IP/Theme already ingrained in them. Those are probably a bit difficult to predict in regards to sales/viability.

Plus, making a full figure, well, isn't easy. It takes a bunch of work to do right.

Good luck!