Good cannabis plants grown for resin are not going to be very fiberous. If you want to try, though, you should look at traditional methods of harvesting and utilizing. I believe it involves soaking fresh stalks in water (and maybe lime?) to soften them, and then rolling and/or pounding them to separate the fiber strands.

You'll then need to weave these strands into cord of your desired size, I think this can be done with a reel of some sort.

Its a fairly ambitious project, good luck!