Facebook Marketplace, and Craigslist are my top 2 places to seach for about anything equipment related, garden, or farm equiment. I will say Craigslist has a better search feature, and will get more hits for a specific search term, while FB Marketplace lists alot of other items, sort of in the same category.
And, proper spelling of said item makes a big difference too. I can't tell you how many things I've found for a buddy of mine who has A-C equipment just changing the spelling from Allis-Chalmers, to Allis-Chamblers, etc. Whether a typo, or misspelled, you do get some occasional hits.
There is also a site called SearchTempest that searches Craigslist ads in a radius of as far as one cares to travel. 4 years ago I was looking for a Brinly seeder for my Sears garden tractor. Located one in Fla. for a really good price, with plates. The guy was willing to palletize, and ship by motor freight. Old Dominion Freight picked it up at his business, and shipped to Cental Ohio for $95. Fortunately, they have a terminal 15 miles away, and I picked it up there, saving another $45-$50 delivery fee. Fastenal also offers shipping, and while they may be less expensive, it was a lot simpler to navigate Old Domion's site for me to set up shipping. Just something to consider, if you're willing to ship. Buyer sets up, and pays the shipping, if you have a way to load, or take it to a terminal close to you, what ever is available in your area.