Serafil thread is used in the cloth-factories. I can shop it in my local fly-tying shop in Norway.
Here is a link for one person that use the Serafil Viktor Sermek
You can also use the Petitjean thread (or any thread that will flatten) and split it with a very sharp needle (scissor point).
This take some more time since you have to untwinn (flatten) the thread. There are some variants to do that are a bit more easy.
One use off Serafil (two cordel) thread is by the shoe repair man. He use a very strong and thin variant off the thread.
So you must go out and hunt for the thread
The thread will do the fly tying much more easy. Dubbing is very easy - just split the thread, apply wax to the 2 cordells and tutch-dubb the dubbing. Rotate the bobbin and apply to the fly. You can insert deerhair,cdc, feather and many more things between the cordells. It is only your fantasy that stops here