Hi Tumbra,
You have not said whether you need just visual 3D models, or functioning models with somewhat realistic dynamic behavior. The latter is what VSTEP, the developer of Ship Simulator, does, but their models are specific to the sea model in the game. They make few military models; many are available only to specific clients.
You may find members in this section of the forum who have made non-functioning 3D models of military craft.
Another possibility is to talk to the research people in the model sections of maritime simulator companies. Many of them are also hobbyists and gamers. They might have suggestions.
In the US, the largest such section that I’m acquainted with is at MSI. They have produced a very large fleet of commercial and US Naval vessels. Here is a link to an older model list:
http://www.marinesafety.com/research/ship_models.php (http://www.marinesafety.com/research/ship_models.php)
It might be worth a shot to write to them. Be very clear as to what you want.
Good luck on your hunt.
Marty