I have looked on Costar for individuals who have done 1031 Exchanges, peeped at alternative websites who act as either a brokerage or glorified listing service, called into my local networks, sifted through hedge fund managers, etc.  

I usually do this by sifting through the Registry of Deeds, probate court files or assessor records.

I see houses daily there, though you will have to sift through a sea of north city houses.

After days of sifting through sources, off market, emails, calling wholesalers etc.

Think about it:  If you have a 3 bed 2 bath townhouse in Woodbridge and list on Zillow/Craigslist, you have to wait for tenants to find it themselves, then sift through all the junk inquiries. 

For the individual investor, you will need to sift through and find a few opportunities.   

There is a lot of great info on BP, it's just important to sift through what is not so great info and take everything with a grain of salt.

I've tried Craigslist in the past and there were just a ton of bad prospects to sift through. 

I am not sure if this is a ridiculous plan but If feasible I will share the process because sifting through the forms there isn't a great deal on the unconventional duplex or just living in a room in SF.

@Richard Wilson Absolutely there is a ton of knowledge out there and sifting through articles and podcasts can get overwhelming at times.