Sounds like a hideously expensive thing to get made to order, the eberspacher idea works well if you can get the ducting in, on my princess 30ds I had to build an extension into the helm position to get the ducting in.
Using the Eber' is plan C, small electric fans are B but element heated screens are the most elegant solution if I can get them at the right price. I'll keep you updated if I have any success.
I think Ford had a patent on it but that it has now expired, not sure how practical it is to make one off or low production runs given the need to arrange the elements inside the custom dimensions etc.
We used small batch produced heated glass on the race cars to good effect and I can see why you are considering it for the boat. It won't be cheap but in marine terms might be bearable.
I have electrically heated screens on the Trader 54. Unfortunately I am nowhere near the boat at the moment so can't get you any more info about them. They work extremely well and are much superior to the Eberspacher outlets I had on previous boat. They never seemed to have the power to clear a sufficient area of the screen.
It is possible that Trader Motor Yachts (01243 375211) may be able to provide more info.