I assume this is like a metal or plastic wheel that engages with a post (or something) and serves to register the print heads? On my Vastex they are metal.
I would just take one off, stick in my pocket, and take a trip to the nearest hardware store and see if they have something the same size.
If no luck at the hardware store, measure the thing and start searching online hardware stores, and the like.
Parts like that were not special made for the press any more than the bolts and nuts were. The good news is that when you find it, it will cost a lot less than if you had been able to buy it from Phoenix.