We need to be realistic. The only way armed citizenry can fight against a powerful government is through guerrilla warfare/terrorism. You're not going to fight a professional army that comes with ISR capabilities, air assets, artillery and heavy weapons by assembling a ragtag of your subdivision patriots while counting on the prowess of the hunting ability of Mr. Eckhardt in a tree to snipe the "enemy" officers. This makes good post-apocalyptic fiction, entertaining movies but it would mean the complete obliteration of your group, all of your family and all your neighbours with just a few artillery shells. Any kind of stand by civilians against a professional army from the most powerful military in the world could only have one result, and it would not be good for the "citizen's militia".
So, the only credible scenario for fighting an occupier/tyrannic government/alien invaders, as proved by countless examples in history of liberation movements facing a far more powerful enemy, would be good old terrorism (once you win, if you win, presumably you can call it freedom fighting), sabotage and other such hit and run tactics.
And once someone crosses this bridge, they don't give a fuck if they can buy their guns at Costco or in the back of van in a dark alley. Indeed, buying in the dark alley is preferred.
Nobody is going to fight the government using legally bought guns while using their government provided callsigns to communicate using their legally licensed ham radios.
So, legal gun ownership as a safeguard against an oppressive government is a fucking illusion, a feel-good excuse to have cool (even if dangerous) toys.
Revolutions and insurrections are made by people who don't give a flying fuck about laws and the current order, and 99 times out of 100, they lose and die in mostly horrible ways.