For everyone who is searching an ISO-Plug:

I found a German site (I'm going on looking for an english site) where you can order an ISO-plug.

Take a look here then click on "Klicken Sie bitte hier" then click on "Online-Shop", then "Einbauzubehoer", then "KFZ-Adapter". Then you see the plug.

There are 2 different items there: One adapter for BMW-install and one "plug only".
With the "plug only" you'll have to cut of the actual plug on your car and wire it to the ISO-plug.

I'll attach a jpg which shows the pins of the ISO-power plug (and the ISO-speaker-plug also, but you don't need it with the Mk2) (hopefully it'll work)

I'll post an english site as soon as I find one.

Additional I asked if the german site is available in english, too and if you can order items from the USA. I'll tell you as soon as I know. Maybe they can tell me some manufactorers.

TeeMcBee