D-I-Y issue:re-charging a/c

Hi there-I own a 99 New Beetle 2.0-gasoline.I would like to re-charge the a/c with R134a.
However, I cannot find a adaptor to fit both the R134a can and the low pressure port on the a/c system.
Or, would I be better to take it to the car shop and let the techs take care of it.

thanks