There is an amazing amount of usable fabric in a mans tie. Just remember, it is all bias. When I was given a sack full of them after a family member passed, I used a light weight fuseable to stabilize them. Since I don't know what size plate you will be making, I still think you might be able to get two blades per tie and maybe three. I guess this is your trial and error period here.
Good luck on your project. Silk does have a mind of it's own.