Just when I was giving up hope on getting new 25.20 ammo, I get a call saying that the order I placed 7 months ago is ready to ship. I spent many a day hunting down 25.20 brass this past summer to no avail. But voila! My order is ready. Too bad it’s $$$, I’m gonna hunt down those spent shells like nobody’s business.
That’s what happens when you shoot a rifle (Winchester 1892, manufactured in 1916) that’s bored in a caliber that was discontinued in the ’30’s.
Cemetery's Gun Blob 
I’ve got one of those babies. But I’m sure the ammo was available into the late 50’s at least. I know I bought it at my local. Somebody’s still making it I’m pretty sure. My 1892 (a rifle) has the strongest ejector in the known universe and throws the cases about 40′ SE each time. But it is a great varmint cartridge for the sneak-’em-up hunter and has accounted for a ton of ’em for me.
Good luck with yours!
When my Father gave it to me a few years ago, I could still get ammo for it at $25/50. The box’s were quite old, with that old school type printing and packaging. I was unaware of reloading at the time, so I was just buy it all up and dumping the cases. Now a box of 50 goes for $60! But since I use it for CAS, I need all lead ammo, and only Stars and Stripes in FL, and Ten X in CA have it, but this year, both of them were unable to get the brass. But I was informed that if I could get the brass, I could ship it to either of them, and they’d load it for me. But I’ve recently befriended someone who can reload, and even cast the bullets for me.