I think I've found a reproduction hensoldt scope mount, but have no idea how to actually obtain it, I found some random real steel repro for airsoft on some japanese airsoft site, the only problem being how to buy it and have it shipped to US.
I have a stormwerkz rail, and it's great for practical use, but half the fun of owning the FNC is the aesthetic,Frankly you would be better off just buying a Stormwerkz mount and then using a stanag adapter to put the Hensoldt on. Not as clean as the original design mount but probably a lot better than messing around with Airsoft.