I am assuming this has a refillable tank and does not use 12g CO2 capsules.
It would be far easier to refill from a fire extinguisher than convert to high pressure air (HPA)
CO2 runs at 850 psi and exceeding this would dangerous.
There are bottles fitted with 850 PSI regulators that are available. I can send you a photo. I expect these would need some joinery.
If you fit a bulk fill adaptor to your rifle and fill to 850 psi with air, you will only get 10 consistant shots.
There is good thread about converting to HPA on the uk chinese airgun forum.
Neil