Look locally / Buy the Seller
it's good advice to look here. i've seen some great cars from fellow members come up for sale in the past few months.
also, try looking in your own back yard. stop by the local porsche garages and tell them what you're looking for. often porsche mechanics have clients who decide to sell their cars and they are the first to find out about it. i got my 2.4S that way.
you might also want to talk to as many people in your neighborhood, friends, colleagues, etc. you never know who has a cousin, aunt or granny right around the corner from you who has a car that's been sitting for years... i got my 2.2T that way. that one was sitting for 24 years.
i've also put up ads at the local supermarket and have gotten many bites (but alas, never the exact car I'm looking for), but you never know who might call, it only takes one good one and you're set.
lastly, if you go the route of buying off the internet, "buy the seller" as they say. due diligence on the seller comes first, then a solid PPI and you should be OK. good luck with the hunt!
my .02