if you have the latest version of T3DGM than you have all the models available that are designed for use by T3DGM. It claims to be able to include third party models (static .X only I think), using the older DirectX 7 format .... very obsolete now that DX9 with shader support is out. If you really really want models, you'll most likely need to make them. It should not take much more than a month to learn how, but maybe a few months more to get good at it.
There are lots of free models out there. Check the 3D forum for more information. So what made you get T3DGM? I played with the demo and thought better about it. Thats what demos are for... try before you buy. GMaker is better than T3DGM but is still too restrictive for me. I bought it anyway because I use the media from the site with PB. Also, the sprite editor that comes with GMaker is good too. You should have waited for the FPSC to be released.
On a side note:
Any DBPro user can make you a FPS kit in a few hours....
it would do...
1 - load HL maps that you create using ValveHammer
2 - Load critters
3 - let you walk around and shoot
things that might take awhile:
traps
doors
health
spells
effects
multiple weapons
But, T3DGM did not have those either