I watched a Extreme home show once and this family built a massive house out of shipping containers. It was massive. Above ground.
People get real creative with these shipping containers. I want to but 4 of them and cut and weld them, bury them in a concrete reinforced foundation. Theres all sorts or vent valves available for panic rooms and such. Same for exhaust fans that can be installed 20-30 yards away to not give away the exact location of the shipping containers.
I know you just want to know where to buy one so you can store some stuff. But whats the fun in that. lol
Theres a few companies in New Jersey that sells them. I have passed the container yard a million times seen the advertisement but never took the number. I will try to search for it.
It will get broken into tho man. Not to jinx you. But a container in the middle of no where, with just simple locks holding those things together, it will get broken into and when you need it most you will go there and it will have nothing. Its the force of nature. People do shitty things. They do sell them for 2-3k tho, and it would cost another 6-8k digging holes and pouring cement and getting vents, welding ( hopefully you know someone who could weld and plasma cut )
I know I have plans on buying 4-6 of them bury 4 to use as a "panic room" and have two on hydraulic system where they lift out of the ground. Ive seen a few rich bastards do this for these Lambo's. The system isnt that expensive. Having the foundation is the pricey part. Ive seen farmers build tornado shelters out of these containers. Wine guys store there wine.