IMHO the cartridge is a dead-end experiment. I doubt it will become a collectible, so the value is as a user. There might be a slightly greater value in Alaska where a bump in factory power could be more critical. Otherwise for someone who handloads the level-of-effort to load 450 Marlin...
The best place to look is gunbroker's ended auctions - look for the ones that actually had bids.
https://www.gunbroker.com/Lever-Action-Rifles/search/completed?Keywords=winchester%201894%2025-35&Timeframe=1&Sort=1&PageSize=48
Yours is tough, though:
* It's been refinished, which limits...
I agree probably not a real one, and I wouldn't fire it. I picked up a few similar at the bazaars in Kabul. Most likely a copy made for the tourists. Nice wall-hangers, though.
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