[FONT=&]Edited to add: Doh! Just noticed OP needed gas almost a year ago. Guess he has it worked out by now....
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I had a set of O/A tanks that were leased in another state, maybe 18 years ago, and when I moved here, to VA, some years ago it never occurred to me to take them back for the deposit before moving, and besides, they still were full of gas.[/FONT]
[FONT=&]When one went empty, knowing there might be trouble, and wishing to avoid the problems that giving too-much-info seems to sometimes make, I just showed up with the bottle on a handcart at the local National Welders / Airgas store in Tidewater, VA, and said "I need to get some gas". The guy just took my tank and gave me a full one, no questions, no answers, no problem. Repeated a couple times since.[/FONT]
[FONT=&]Then I got a MIG and needed some C25. Went to Airgas and paid for the gas, plus a tank lease or purchase, I don’t remember which. So when I ran out of C25, I happened to go to Arcet instead of Airgas (was giving a buddy a ride and he was an Arcet regular), and so took the C25 tank there and the guy just swapped the empty for a full one, no questions asked, even though the tank had come from Airgas a few months prior.[/FONT]
[FONT=&]You are near DC? I don't know where you went, if it was in DC, VA, MD or what, but it might be a state law thing, and in DC the laws can be tight of lots of things (go figure...)[/FONT]
[FONT=&]There are both Airgas and Arcet dealers just south of DC in VA, and I've had no problem in VA. Maybe a coincidence, but it also may be that rather than doing the whole explaining-in-detail thing on the phone or in person, just carry your tank into the store (I take a handcart and a rope to secure the tank) and say "I need another bottle of gas." And see what happens. It may be less convenient than checking price and availability on the phone, but if it works, you will know where to go from then on.[/FONT]