Where to find sources
Try HARO (Help A Reporter Out).
Tweet a journo request using #journorequest or #sourcerequest on Twitter (these get retweeted by other, bigger accounts such as @journo_request and @PRJournoRequest).
Twitter bios. LinkedIn. Google Scholar (most papers published in peer-reviewed journals have emails listed on them).
Google search, email/DM sources. (Hopefully, this goes without saying: while it’s fine to follow up on your request, please don’t harass sources.)
Ask friends, ask family.
Ask your editor.
On interviewing
Q&A: Larry King on asking simple questions and listening closely (CJR)
Is Larry King too soft on his guests or is it his “softness” that prevents knee-jerk defensiveness and encourages openness? Soft Questions? Larry King Explains His Interview Style (The Young Turks, YouTube)
Mike Dronkers’ TED Talk, ‘How to Interview “Almost” Anyone’ (TEDx Talks, YouTube)
Interviewing Principles (Columbia Journalism)
After the story is published
This is just my two cents: aim to send a published link/PDF to the people you interviewed, thanking them for their time and inputs. And, down the line, aim to check in with former sources where and when you can. Not solely because you can get a story out of it, but because it’s also just polite.