Well, from
fps-files.com here are a few tanks...
http://fps-files.com/download.php?view.149
http://fps-files.com/download.php?view.462
http://fps-files.com/download.php?view.583
http://fps-files.com/download.php?view.585
You should be able to find something here, in the
Entities section there's a wonderful APC and such available...
http://www.fpsfree.com/
In the futuristic, military vehicular area you might want to check out
Cosmic Prophet's brilliant and extremely generous Mega Sci-Fi Packs.
Here's Part 2, it's got everything Part 1 had and more, you surely could find something in here...
http://forum.thegamecreators.com/?m=forum_view&t=142154&b=24
Short of all that, you'd really
really benefit from checking out the GC Store built into FPS Creator. Yes, this would cost money but you know you'll be getting top quality work (not to say that any of the models I linked you to previously weren't top quality, because on-top of the fact they're free, they all
are done well. I digress - anyways I type
vehicle into the search bar in the store, and I count 28 awesome looking models. If you're looking for an
excellent tank still, you definitely want to check out Kasseyus's
Russian KV-1 in the store. But it's full of all sorts of other magnificant models too, hummers and planes, to a wicked helicopter (DarkOwen's
Apache) and military trucks to a whole
set of future based alien military vehicles from Rosstradamus's
Mech City collection.
I mean, I hope I haven't led you on a wild goose chase to check out all these models and find nothing that's quite what you're looking for, but that is an insanely cool and well-done assortment of military vehicles from our generous community at large.
Hope I helped a little, take it easy man.
Cheers
Life would be much easier if I had the source code.