Apart from www.samstagsales.com/vwaudi.htm I found a couple of more places to order the radio removal key: http://www.gprparts.com/sirtools/tools_VA.html (va6026)
and http://www.zelenda.com/VW/beetle.html (T10057).
Also a couple of funny pics of the tool :-) : http://mach.mach-nine.com/gti/pictures/ and maybe the real one: http://www.gprparts.com/sirtools/images/VA%206026.JPG

I cut up my own keys from an old credit card, looking at the above URL, hoping that the picture shows the keys in true size. However I could not unlatch my factory HU (golf'01, no Monsoon, no Mid) to see if I'll be able to plug one of those adapters on the back.

Does anyone have any other tips on the key, such as size or the position in which it should be used? (small slot pointing up?). Thanks