Our club uses a local fire extinguisher shop. They do a good job for a good
price and they do it in house, ie, in a couple of days. When we've used
industrial gas suppliers they have shipped the tank to a newarby city and it
has taken a coupel of weeks.

Note that all regulation for compressed gas tank come from the DOT. I don't
think the FAA has any regulatory involvment with them.

John Scott