Because of privacy laws, lenders are not allowed to call you when a loan goes into default or might be foreclosed.
The best you can expect is that a lender might give your card to a borrower in trouble, as someone who might help. This is certainly a good strategy, and you should pursue it with local real estate lenders.
After foreclosure, lenders and servicing companies generally rely on real estate agents to market their properties. Learn which companies in town are the preferred brokers for foreclosure properties.
Get to know the agents. Once you establish your credibility as a serious buyer, ask them to notify you as soon as something new comes into their inventory. This gives you a head start before the other buyers see the ads.
It also saves the agent some advertising and marketing money if you buy before those expenses are incurred.