I've known what to look for, but in 8 months of searching, I've only just found ONE! It seems like a fab stone, but unfortunately, much larger than what I want. I've found a second that comes close, but isn't quite an FIC.
I did look at that other thread in your link, sounds like DCD might be the spot to keep looking (that's where I found the one I mentioned too). Wish I could see it in person, just to get an idea what it looks like compared to TICs...
A FIC has a combination of a rather shallow pavilion with a steep crown-angle and a high crown.
So, you need a rough stone, that is rather flat on one side (where the pavilion comes, while it maintains a high diameter on the other side (so that you can get a steep and high crown).
In reality, you will not find many such rough stones.
Of course, one could also use a rough stone with a less shallow pavilion-side, and just cut it more shallow. But that sounds very un-economical to me, and that is why you hardly find such a FIC.
This could change if people would start paying immense premiums for such a stone. So, if you are ready for that, just let me know.