The problem is to maintain the private citizen/armed forces of a cou try balance of power is ludicrous. What exactly do you need to buy to defend yourself against a troop of Navy Seals? OK, training and gear. For a start: Teflon coated bullets, high velocity rounds, grenades, land mines, high explosives.
OK next step. What do you need to defend yourself from an armored tank division?
The 82nd airborne?
A harrier jet?
Sorry, but once the military reached a certain point, it's impossible. And trying makes you sound like a madman.