My "salvation" has been a company in Hollywood, Maryland, named "Quality Cartridge Compny" (https://qual-cart.com/index.html). I'm getting kind of old, and many of my few firearms are even older, and for years the calibres I cast for, reload, and shoot are never available either in store shelves or mail-order! Quality apparently recognized the need -- and manufactures quite a few obsolete (to many ) calibre cases. Buffalo Arms also purveys some, as well as Graf & Sons, albeit many of Graf's are in fact Quality Cartridge products.
... A source I found, use, and have never had a bad experience with! The only "down" side is on occasion one must wait a few months until they run another batch of the calibre you elected... but this is but a very minor issues.
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