Can’t help on the Screw Cap (p/n AD415) but I bought a secondhand hopper plate from a different machine off eBay that is close enough to do the job.
The feeder tube is of a slightly smaller diameter than that on the original Hopper Plate (p/n AA513), and could be improved by using a stainless steel collar of the correct ID/OD. On the positive side it’s made of much heavier gauge stainless steel and also includes a built-in guard above the feeder tube.
If you can source the Screw Cap - which is the bigger challenge - let me know and I can send you the hopper plate if you’re interested?