Well, obviously, you talk to people with gutted houses.
The question I suppose you're asking is: How do you find them?
A few may be listed on the MLS. Try "handman special" and similar terminology.
A lot are in foreclosure. What happened is that someone tried to rehab a home. They got partway through, then ran out of money. When those come back on the market, they'll be in the MLS, too. But then you're buying from the bank, not from the seller.
Contact hard money lenders. They'll have made loans on some of the rehabs. When the rehabber ran out of money and couldn't repay the loan, the hard money lenders foreclosed. Because the hard money lender lent at about 65% of after repair value, you should be able to get some for a good price. In fact, if you have rehabbing skills, the hard money lender might lend you the money to continue the rehab.
Also, check your local court dockets for contractors suing homeowners for non-payment. In some cases--as with the rehabs mentioned above--it's possible the homeowners ran out of cash for the renovation or rehab. In this case, contact the homeowner.
Hope that helps.