incrediBILL - 4:59 am on Sep 16, 2013 (gmt 0)
Building a link network is fine if you can also build traffic, otherwise it's kind of a waste of time in the Penguin era.
You can buy dropped domains
The easiest way to do this IMO is to find a directory of blogs and just link check the outbound links about every 15-30 days and you'll find them dropping like flies. Finding them before someone else does is the key because you want to catch them before they land in a domain auction.