I'm not sure where would be best to find the connector. The connector isn't only for the 6WB, my factory cluster actually already had the same plug. Looking on something like ebay and searching for "Most Fiber Optic 2 + 12 Multimedia Connector" I see two used factory ones in the US that I think would work. Maybe check ebay, or similar, in Europe?
On the HUD, I'd check this out:
https://x3.xbimmers.com/forums/showt...t=hud+retrofit
It shows where the HUD connector would be. I'm not sure if you can add to the 6WB or not, but I'm guessing it's similar? Maybe you can use the part from your old cluster?