I sold my .25-25 reamer to somebody several years ago. You might post a WTB/B/R and see if he’s still around and done with it. Can’t remember if it was here or Cast Boolits.
I would think somebody good with boring tools (like a lathebore mould maker) could reproduce the straight taper in the rear of your sleeved chamber and blend it in with the remaining front part. Or you could make a “D” reamer to accomplish same.
I fixed the mangled rear of a .22-15-60 chamber by drilling/boring the bad part out to fit a 3/8” diameter piece of turned .22 caliber barrel steel. It was maybe 1” long, turned concentric with the worn-out bore.
I turned a piece of graphite rod (“borrowed” from our Glass Shop) to fit the remaining chamber and bore, and to fit the .22 barrel. I tinned the surfaces, put in the graphite rod, heated the pieces, and pressed the bushing home, with the graphite keeping everything concentric.
When the setup was cool, I drilled/busted the graphite up, set the lathe compound to the angle specified on the .22-15 chamber drawing in Kelver’s Pope book and bored it out until it was continuous with the remaining chamber in front. The rim seat was cut with a lathe tool as well.
I had to make a reamer of sorts to take out an invisible obstruction (best guess a little solder that had come up out of the front of the bushing), but after that, my precious hoard of shells chambered, fired and extracted normally and with no marks on them.
I will have to say, as an Experienced Shooter of the class of freakishly long cartridges (.22-15-60, .25-25 and .40-90-3-1/4”), trying to make target quality loads in these calibers will soon dispel any anguish about how Original the specimen you’re playing around with is. You will have other and much more annoying fish to fry.