Ha, I just buy a case @ Sams Club once a year.
If I was limited to only 1 firearm I’d probably go with a handgun, because that’s the one you can conceal on you every day. It’s there when you actually need it instead of at home in the safe. California may make it hard to CCW but not impossible, esp if you don’t care about following laws. I’d probably be paranoid enough to take the extra steps of sourcing from out of state even if that means an 80% glock frame shipped to a friend. Use a prepaid card or something that isn’t tied to your name and address. etc.