Rich,
I have spoken to Fred at Chorley Auto Volk 01257 266574 and he says that he got my idle screw from VW main agents. If you can't get the part, ring him with your engine and VIN number and he will look the part number up for your specific model.
I did tell him that he may get loads of calls from here and vwgolfmk1.org.uk members but he didn't relly seem to mind!!
Hope that helps, Dan