Well, then a new amendment should be passed that places some reasonable restrictions and addresses this issue.
I can't give you a clear answer because I don't know what it is. I want rules that let large militias pool resources to purchase gear and armour.
What I don't want is billionaires buying their own tank fleet or corporations buying their own private armies.
So I don't know what the regulation would look like, but it would probably involve registering as a specific type of organisation that excludes corporations. For example, you would have a limit on how much armour and gear you can buy as a large militia and you must have no business ties.
You might register as a militia and publicly disclose all your finances. You might be a kind of non-profit and subject to tax-exemption. So a corporation couldn't be a militia.
You could then have certain tiers roughly equivalent to different parts in the army, e.g. fireteam, squad, section, platoon, company, batallion, regiment, division, corps, etc.
You could have a certain upper limit on what kind of gear you can have. So, you can have x number of tanks in a certain militia of a certain size.
That would also come with certain regulations, e.g. government officials can come and check up on you every so often, you have to have a place to store all your gear and vehicles securely, you should try to keep everything well maintained, etc.
I'm just shooting off ideas here though.
I will say that I consider the infringement of rights to be a bigger deal at this moment than the possible loopholes with regards to billionaires and corporations. I would rather the right to bear arms be allowed to be exercised first and then implement some amendment or law which allows you to regulate everything after, with regards to corporations and billionaires.
What should happen is that regulation should be imposed universally for all firearm users. That means background checks, tests, training, and every so often a checkup from law enforcement to check that everything is being stored and maintained safely.
I think that people should be able to use hunting rifles with help from an adult when they're young, sure, but I think even private transactions with sidearms and larger caliber, non-hunting equipment, should be subject to regulation.
So that means that your dad can show you hunting, but if you want to use your own pistol or use any hunting equipment on your own or automatics on your own, you need to go through the background tests, training and checks.
I think that it shouldn't be a background test to buy a gun, but background tests and checks to certify that you can safely exercise your second amendment rights without being a danger to your community.