Good advice, especially from Bill and Lori.
Here's the approach I'd use:
First, market for homes not on the market. Lori suggests this. I'd just take it one step farther. Market especially to non-resident owners. People who own houses but are renting them. At some point, those people will sell. Sometimes it's just time to sell; other times, it's after one or more bad experiences with tenants. The owners become "don't wanters."
You want real creativity? Go down to your local courthouse and get the records for "unlawful detainer" and other court actions and evictions. Contact those owners. They're very likely "don't wanters."
Second, contact people who have listed their homes for rent. Make them offers.
Third, market on services such as Craigslist. You'll get a lot of flakes, but that sometimes works.
Fourth, contact lawyers who handle estate sales.
Fifth: Make lowball offers on those overpriced homes that aren't moving. (There's no real definition of "lowball," and in fact maybe you just make a reasonable offer. But I'd go low.) At some point, those sellers are either going to give up or give in. Your odds of succeeding are quite low here, but it's all a numbers game. Let's say you find 10 houses that really are each worth about $600,000. But they've been priced at $700,000 or more and have been on the market for at least 90 days. Make offers of $500,000. See what happens. The worst is: Nothing, but that's what you've got now. The best is: Your offer is accepted. The next best is: Your offer is countered. And that's great. It means the seller is open to negotiation.
Finally, there's nothing wrong with the "personal approach" you suggest. In that case, identify a specific neighborhood you're interested in. Then find the agent who "owns" that neighborhood. Typically, in most neighborhoods, there's one agent (sometimes two) who really is the 800-pound gorilla. You can determine that, in part, by driving through the neighborhood and looking at the "For Sale" signs. When you see the same agent's name on half the signs, that's the one you want. That agent should know the community like the back of his/her hand, and if anyone can give you an edge, it's that agent.
Hope those suggestions help.