[Those aren't *rare* rifles you mentioned…]
Few stores in Canada were given. GunBroker and import.
Otherwise, network. Go to shows, go to shoots, join a military historical society or something. When the time comes to sell something rare, it's usually ‘Oh I remember Lennox said he wanted my rifle if it ever came time to sell. Guess I should give him a call.’ The EE may be full of usual No. 4s and re-furb Mosins, but aside from that it's a secret fraternity and to gain entry requires that you put in some time to meet people and ‘prove’ you appreciate the history and you're not just in it for quick cash.
Careful with auctions, as many have found it's where problem guns get sold: the owner is insulated from criticism by not having their name attached, and of course all lots sold as-is. Another trick is at a gun show table, guy says it's not his; he's selling it on behalf of an acquaintance, or he just took it on trade. (He's basically trying to dis-avow any problems from the get-go.)