How do you find information about government employees or contractors?

I’m trying to find information, specifically salary information, on someone who might be suing me. I know that they are either a federal employee, or a federal contractor. I know the GS salaries are easily available online, but first I have to know their GS rank. Is there a way to find that out? For contractors, are the contracts public records, or available via FOIA requests?

All I can seem to find online are the websites which give me basic information I could get from a phone book, then try to charge me for more info.