Where I live, I couldn't find anywhere that sold it to individuals. They needed a business license. Also it's tough to get it delivered and hide it if you live with family or other people.
I was searching for places to buy filled inert gas tanks online and struggled initially because most online vendors I found that didn't require a license/registration only sold empty tanks. However, in the end I was able to find 40ft^2 and 80ft^2 (filled!) tanks of compressed argon—not nitrogen but still an inert gas—available for anyone to buy on a
very popular online shopping/e-commerce website. The gas tanks had many positive reviews from people who used the gas for welding purposes.
Some people in the reviews said that because compressed gases are classified by USPS as hazardous materials, they had to drive a long time to a FedEx location to pick up their tank rather than get it delivered all the way to their home. This could potentially be a good thing in the case of living with others, since someone could hide the tank in their car initially and sneak it into their house when others can't see. However, the majority of customers in the reviews were able to have the gas delivered directly to their home without issue.