Capturing factories only adds a multiplier to your tax income per tick, it has nothing to do with that.

Speaking from my experience, there are no other ways to get MRAPs/APCs/Tanks other than to capture them from BLUFOR/OPFOR. What you can buy from the menu is all there is, and it won't change.

On the side note, capturing sea ports does give you a discount on purchasing those vehicles, but again they do not give you extra options of what sorts of vehicles you can buy from the menu.

ok thanks , i just tought that i may be stupid and there is a way