There is a paintball shop in Brackenfell in the industrial complex next to the Okavango bridge called Dye-Hard (www.dyehard.co.za). They sell the 9oz canisters for the qb79 for R190 and fills them for R1/oz.
After reading on the internet it seems you can get between 300-500 shots out of one fill. People's shot count varied probably due to heat and initial fill capacity. It does seem that you can get at the very least 300 full power shots (+-600fps) from one fill.
All in all the perfect poor man's PCP
On a side note that rifle's crude open sights are to my amazement very accurate. Once again that old saying of "Don't judge a book by it's cover" came to mind after using this budget pellet gun.