I bought mine from Hughes, but they are simply common industrial parts that can be had from Graingers etc. The locking screw does not touch the distributor shaft, rather is constricts the collar so it grips the shaft.

A secondary reason I run a collar is that it dramatically reduced the wear on my bronze gear I used to run on my roller cam. It did that by limiting the intermediate shaft gear climb up on the cam's gear, which also alters the position of the rotor as it goes up and down, ie bouncing timing at idle.

If the intermediate gear is allowed to travel up and down excessively, the contact pattern on the gear's teeth changes significantly resulting in accelerated wear. Once I started running the collars, the wear pattern stabilized and my gear wear dropped dramatically. It also stabilized my timing at idle, as we all know the intermediate shaft rotaes a bit when installed or removed due to the angle of the gear cut. It's attached directly to the rotor, and as the shaft rises and falls when the motor is running, the timing alters slightly. I imagine that the gear is forced downward into the bushing when the motor is under acceleration, but at idle is moves up and down limited only by the tang on the distributor shaft. The motion reminds me of how my driveline "bounces back and forth" when cruising under no acceleration load or deceleration.

Be advised that some clearance between the collar and intermediate shaft is required, or it will wear the intermediate shaft bushing until it machines the clearance it wants. I have just left the collar loose enough and added a small "washer" of paper(like a matchbook cover" just below the collar, so that it positions itself once the distributor has been fully seated. I then re-pull the distributor, loctite the screw, tighten it fully, remove the paper and re-install the distributor. I have not had one move yet. If the set screw comes out, it would be flung into the motor possibly between the gear teeth, so clean the oil off it and loctite it.