9.3 Cylinders
The compressed gas shall be stored in a commercially manufactured gas cylinder of appropriate design,
specification and certification. Except where the maximum storage pressure is less than 50psi (3.4bar).
Some events may have further restrictions on bottle sizes/ weights used, please contact the event organiser
for clarification.
Most people use the 2Kg Aluminium CO2 bottles with screw valves fitted. I would recommend adapting your design to use the newer bottles that are easier to get hold.
Of course if you are able to get your current bottles re-certificated then that would also be acceptable.

The thinner bottles tend to be steel and these can corrode quite badly over time resulting in failure, especially if moisture has been allowed into the bottle (e.g. valve left open for period of time).