religiously search craigslist... I use search words of weed, weedeater, chainsaw, chainsaws, chain saw, chain saws, trimmer, trimmers, blower, blowers, homelte and poulan you get the drift... or simply put up a wanted add for unwanted weedeaters or chainsaws cash paid, you'll usually come up with something, I think I was the first to do that in my area and now they're on there all the time so it's harder to get them that way but it does work.

that's been the source of almost all of my engines in the last few years, the rest are garage sale or friends giving me a load of them. every now and then you'll get a small engine shop or second hand tool store that's going out of business or doing spring cleaning and you'll get 20 weedeaters and a couple chainsaws for $50, or 7 chainsaw engines for $90 (recent deals I've gotten). also if you are handy with the engines and getting them running put up an ad on craigslist offering your services for $40 plus parts (shops charge $80 plus parts usually), you would be surprised how many engines you can end up just getting out there...