I agree with networking and talking to people, you get to meet real cool people doing that. And like you said, if you help someone out of a bind or fix something or they know you tinker with small engines - they'll usually throw something your way. Oddly in my case it's rarely ever saws, but mostly burned out trimmers. (sometimes it ain't easy livin' with CAD!)
I do believe it very much has to do with location though. You almost never see 60 - 100cc saws (at least here) pop up, unless you live someplace near the PNW or get really, really lucky. I think the more middle of the country you get, you have a better chance of finding something like that. But then there are some places, even older shops that have forgotten or never heard about McCullochs. (if it's not the current market it doesn't exist)
But it's good to be patient, you never know when something will show up. On my end I've been searching off and on for 4 - 5 years for the one I've been after. The whole "One man's trash..." is a real thing, so I know it'll turn up sometime.
But the upside is at least you get to meet people and sometimes come away with something you didn't know you needed, a different point of view or learn something, especially with older folks.
