CO2 tanks require a pressure test and inspection and then the body is stamped with date...it is good for I think 2 or 3 years...from that date.
I find it hard to believe that in VT they are not allowed to fill any CO2...wow...so every fire extinquisher, soda and beer machine, paint ball shop, and welding company has to buy their CO2 out of state??????
Down here you have a few choices though
1- Welding supply shop...generally drop it off...they fill it...I pick it up the next day or in afternoon as they do their big jobs first and let mine sit for a bit.
2. Fire extinquisher and safety shop.....they just re-tested my tank, installed a new seal around neck...and filled it for $26. Do it while I wait or I can drop off and pick it up later. Easier if you have an exchange tank to swap out...but they restamped my tank with new cert dates so I am good for couple years now.
3. Shop that supports home brewing.....or soft drink distributor....they cant inspect or test tanks but with a valid date on cylinder they are authorized to fill it....but not sure the cost of food grade CO2 is worth it if more expensive in your area.
4. Paintball shops...expensive...they are used to selling little canisters for guns for $10 each and try to apply that same cost ratio to a 5lb cylinder...they are smoking crack.