I would advise that you look at FE36 (a Dupont product common in many automatic extinguishers). They stop the fire by acting on the combustion process through a chemical reaction, rather than directly smothering the source of ignition and thus oxygen starvation.
Looked at those and could only find 2 UK suppliers who would send them here (dangerous goods carrier needed) and the cost would be around £175 for a 2kg auto. We then have the problem that the gas not available here for annual service or recharge so postage back to UK around £40 each way.
There is alos anothe "new" gas, FE200 but that's also not available here.