Rossi Rifleman

Where can I find scope mount bases to fit the 1 1/8" OD barrels of the large frame top-break single shot rifles, like the combos and Trifectas? What is the Weaver base number?

You can find one, on eBay.
https://www.ebay.com/itm/124179256629

The one From weaver has the following information: .410/.22LR & .410/.17HMR SMALLFRAME MATCHED PAIR COMBO ONLY
Note 7
Base Pair: 48492
1 piece: 92A(48092)

Note 7: BASE DOES NOT FIT ROSSI LARGE FRAME MATCHED PAIR COMBOS (ALL MODELS WITH 20 OR 12 GA SHOTGUN BARRELS)

Thanks. That's about what I concluded. I do recall that years ago a scope base was included in the box when you bought a new Rossi single shot no matter what the caliber or gauge. I ordered one for the smaller barrels and will somehow figure our how to modify it. It appears the screw spacing is the same on all barrels so that will make it somewhat simpler.

Would scope bases made for Wizzard barrels also fit the earlier Trifecta and other 1 1/8" diameter Rossi barrels?

The one from eBay might fit.

I did just spot one on fleabay for a Wizard. Info from the seller leads me to believe it will work for the Trifecta 1 1/8" diameter barrels. I bought and will find out.

I now see it's the same one JRexA pointed out above - and yes, though listed for a Wizard, it fits well on the 1 1/8" diameter barrels of the Trifects