Well any garage with air con facillities, should be able to do this for you. Its just a case of pluging their machine into the system and withdrawing the gas.
They will probs charge you though!!
Or you could accidently loosen one of your air con pipes off, (obviously as you dont know what you are doing

and accidently allow the gas to escape!!!! Although that would be naughty!!
Stand well back as you dont want to be breathing the gas in, while you ponder over just how that could have happened.
You with me on this?:rofl: