Find out where your local auctioneers publish their advertisements. Look in your local newspaper, free classified ads, or weekly junk mail classified ads. Around here they don't advertise in the paper, they use the Wednesday free junk mail ads, which seems funny to me, but that's what they do here.
Once you figure out where to find the auction ads, keep your eye on them every week. They usually will publish a partial list of interesting items in the upcoming auctions. Go to any auction that advertises a tiller. These usually have 5 or 8 horse briggs side-shaft engines. As a bonus, if the tiller is a piece of crap you can usually win the auction and take the engine home for next to nothing.
I saw an auction listing a couple of weeks ago where they were selling two tillers and a water pump. Too bad I was broke at the time so I didn't go....