1) pending delete auctions. These are domains that were not renewed and are going through a pretty complicated drop process. You can backorder these names at the auction venues and then each attempts to "catch" the dropping domain. If one is successful you win the domain at $59 if you're the only one to backorder the name. If more than one person backordered the domain a 3 day private auction is held. Once the domain goes through the drop process, the back links have pretty much zero SEO benifit to the new domain owner.
Apart from pending delete and auction domains, you can use our domains crawler that lets you scrape websites in bulk to find domains that are available to be registered and have amazing backlinks. Your personal crawlers run on our servers and are entirely web based. You do not need to install any software or have a VPS or proxies in order to do use them.