If one wished to use pure nitrogen in the tires you could get a tank of
nitrogen from a welding gas supplier. The half size tanks are sold, not
leased.
I have one left from when I was running Citrokn cars. I used it to
recharge the "spheres" (accumulators) in the suspension, steering and
braking system.
A regulator is not needed if you exercise reasonable care. I have a 1500
psi gage between the tank valve and the hose connection as the highest
pressure used in the accumulators is less than 1500.
For tire inflation purposes you would only need a gage higher than the
highest tire pressure you anticipate filling, like 100 psi. Gages are
most accurate and easy to read in the middle of the range.
If you wish to be absolutely careful you can use a regulator or a relief
valve. I did not as the Citrokn accumulators would easily withstand the
initial pressure of the nitrogen, about 2300 psi. Tires, of course, will
not stand such pressure. New tires are supposed to withstand 4x the
maximum rated pressure (140 psi for a 35 psi tire; 240 psi for a 60 psi
tire; 320 psi for an 80 psi tire). A steel rim should bend at the bead
seat before the tire would burst.
Air is largely nitrogen, about 4/5. It's the rest of the air, oxygen,
trace gases, and water, that are not needed in the tire.
A considerable benefit of dry nitrogen in the tires is no wheel rim rust.
Nitrogen molecules are large enough that they do not permeate the tire
liner like lighter gases. Helium even leaks through the steel of its
tank.
After purging the tire several times with nitrogen there should be almost
no oxygen or moisture left inside the tire.
Al