I’d be tempted to find a local machine shop with a wire EDM and have them split your extractor into two ejectors. I’m not exactly familiar with Ithaca ejectors and whether there may be other differences between extractor and ejector barrels, so please don’t hate me if that’s nonsense.
The only problem I see here is that wire edm cuts are not like a nice clean scalpel cut where material can simply be split with zero dimensional loss. You have to factor in kerf width and surface roughness, that will then need to be machined and polished off.
Sorry, but I can't tell you the best way to disable the ejectors on a Flues Ithaca, and simply use it as an extractor gun. But that sounds like a good option until you can find or have well fitted ejectors made for your extra barrels.
