There are several ways: (google is a great tool. but also use alternative search engines. I've found guns using "Yahoo" and others that didn't turn up im google.)
1). Go to google and search "HOLTS Auctioneers past auctions" and the gun name you're interested in. You'll get references back to about 2005. Ultimately you'll come on a site that gives a comprehensive list of past guns auctions.
2). Or go to Barnebys, go to "category" and select "Arms & Armor" and search the name you're interested in. If you can get a gun to come up, click on it....there will be a little note that says something like "all guns can be seen in Arms & Armor." Click that and all guns of that name will appear by auction house reference - Holt's, Sotheby's, etc.
https://www.barnebys.com/auctions3) Lot-Art is also an auction house compendium. It doesn't have as many arms and armor reference as Barnaby's but can be helpful. Get on their mailing list.
https://www.lot-art.com/auction4) Check out "Proxibid" and "Invaluable" and "liveauctioneers" as well - compendium sites -their addresses are listed below. (just click on them).
5) Here are some auction house websites if you want to manually search them:
AUCTIONS:
US:
https://montroseauction.comhttps://www.rockislandauction.comhttps://www.amoskeagauction.comhttps://www.gunauctionsusa.comhttps://morphyauctions.comhttps://www.poulinauctions.comhttps://www.proxibid.comUK:
https://www.ryedaleauctioneers.comhttp://www.scotarms.co.ukhttps://auctions.holtsauctioneers.comhttps://www.southamsauction.co.ukhttps://www.lot-art.com/auctionhttps://www.barnebys.com/auctionshttps://www.wilson55.com/https://www.thecanterburyauctiongalleries.com/homehttps://www.bonhams.comhttps://www.liveauctioneers.comhttps://www.invaluable.com/auctions/Guntrader is the UK version of Guns International or Gun broker. It can be clumsy to use since they insist on your using a pre-set series of gun types. You can't just search for "Reilly" on their site. But if you put the gun name and "gun trader" in a google search, you get a list. Past entry's however are not archived.
https://www.guntrader.ukGunstar is also a UK site. You can key word search it but there are not as many guns on it. It also is not archived.
https://www.gunstar.co.ukFRANCE: (For current sales. The auction site can be clumsy since it insists on your entering a gun name from a list; if the gun name you're interested in doesn't appear in the list, search in google the "name" + "naturabuy" - sometimes past auction ads will come
https://www.naturabuy.fr/annonces-chasse.htmlITALY: (Czerny has catalogs listed back to 2000. . .I've had a hard time registering for their site: they want passport info as if you're going to bid.
https://www.czernys.com/catalogues/