I found this AD on Kijiji for CO2, O2, Argon tanks. I picked up an O2 tank for a reasonable price. The guy is very friendly and has many tanks available. I told him I would share his ad with the club in case anyone is looking for a CO2 tank.
Good stuff. Make sure co2 tanks 10 lbs and over have an handle, as @Yac.b pointed out, some locations (Guard-x) may refuse refills.