Do you sell adapters to connect a CO2 regulator to a mixed gas cylinder?

Adapters shouldn’t exist for that, CO2 cylinders and Mixed Gas cylinders work at different pressures.

Mixed gas works at significantly higher pressure so attaching a CO2 regulator would at very least damage it and could also be very dangerous, which is why they have different threads.

I.e. the different threads ensure you are connecting the correct regulator for your cylinder.

You will need a dedicated regulator for mixed gas.