Thank you, M35A2-AZ and MyothersanM1 for your help.
Just called Cummins with the part number. According to their computer, there are none in stock in any dealer in the continental US, the "factory" does not have any, no estimated production date. There are some at a dealer in Belgium, can be delivered in a few days, price just under $140 not including tax.
Which is interesting, because similar parts from Parker and others are in the ten dollars range. I also asked about a Cummins-branded dual fuel conversion, the guy said he had no idea what I was talking, no such animal.
So... anybody got a local dealer with one of these valves in stock for a reasonable price? Maybe a take-off from a scrapped engine, out of a scrapyard, or other source?