There is a (un)loader that has at least one military vehicle. I,m at work so I can,t check. I believe it is from Trainz pro routes and is built in to 2010 upwards. It has a large number of commodities and the vehicle section is down the bottom. Do a search for "LARS" in the buildings tab. and you can easily configure a flatcar to carry it. Post here if you need help doing it. As a further footnote you can also configure the wagon to be loaded with the tank, battleship etc! in surveyor
There are a couple of tanks. Phil Skene uses them in his LARS/ProtoLARS Tutorial. There's probably a lot more. A search on Category - Commodity and Name - Tank (or whatever) should show what's available.
