I've never seen Sodamistic mentioned for CO2, so I thought I'd post to give everyone another option. They're located at Hwy 27 & Steeles, so it's pretty close to Camcarb. If you can make it to Camcarb during M-F business hours, you can probably make it to Sodamistic. They sell all sizes of CO2 cylinders, and refill any size as well, paintball too. I bought a 5 lb aluminum tank, filled, for $82.50 + tax (cash only, people!). It's not as cheap as Norwood Fire, but Norwood didn't have any in stock, and the one they offered to bring in for me was steel, not aluminum. And they're much cheaper than Camcarb over at Steeles/Weston (Camcarb wanted $110 for a 5 lb). The refills at Sodamistic are 15.99 for a 5 lb.
The address is 37 Baywood Rd, Etobicoke. 416-747-7810
Here's their website and pricing.
Hope this helps!