My R reg 1998 Mark 4 Golf needs a new roof aerial base. does anyone know where can I find one apart from a main dealer or breakers yard?

The problem I have is I cannot get MW reception at all. FM is quite poor also. I have taken it to my local garage who are excellent they have checked all wiring etc. I've been told the problem is atthe base. The guy that looked at it rang local VW and was told this model is unusal as it does not have an amp in the roof. It's one of the very first Mark 4's.

Any help comments would be appreciated. Many Thanks