I had to buy a replacement regulator and adapter when I used a pub bottle - it was completely different regulator to the one for the disposable bottle.
When I ran out of pub gas, in an emergency, I had to use a disposable bottle of Argon mix. The difference between pub gas a proper shielding gas is worlds apart and no way would I ever consider going back to pub gas. I now have a rent free bottle from SGS.
100% CO2 Has it's place in the workshop.
IIRC there was a posting a few month's back asking the same
question, with suggested suppliers of the adapter.
Here is one: