If you want to understand certain job roles, there is a repository of interviews with people in many different roles at www.jobshadow.com. This repository has interviews with people in a variety of professions, including a radiologist, a truck driver, IT Manager, football coach, and crime writer. This is not a substitute for speaking with people in those roles, nor is it enough to build a persona, but it's a great start, and way better than nothing, or relying on assumptions. Another thing to try, to learn about your intended audience, is to seek out bloggers who write about what it's like to be a (fill-in-the-blanks). Certainly you will only get their perspective, but you can glean a lot of basic information to prepare for those initial interviews. Podcasts are also a good source of slice-of-life information and interviews with people in particular roles.
I have done this to better understand motorcycle culture when I was researching motorcycle insurance, and to understand the pain points of over-the-road truckers when I was researching fleet telematics. It's a great place to gather enough data to develop a research plan, and to start understanding the role of your intended audience.