I had some questions about investigative technique, so I googled private investigation firms in my city and chose one that looked good, then emailed them briefly asking what they'd charge to answer a very basic and narrow question. I got a reply on the same day from an investigator saying their ongoing consultancy rate is $150 an hour plus expenses, but if it's a simple question he can answer off the top of his head, he'd do it for free. So I told him the question, and he wrote four medium-length paragraphs in response and didn't charge me a cent. I now know what I needed to know. I also had questions on family law procedure, so I picked a lawyer I had casually chatted with years ago, when she had been a sharp young junior. Today she is a partner. I mentioned having met her and congratulated her on the progress of her career and then asked her if she could answer some simple family law quetions. She thanked me for the email, and said she'd love to help me, but she does only employment law. So she referred me to another lawyer she knows personally who does only family law. I emailed him the question, and it looks a lot like he's going to answer it simply and concisely, again without charging me any money for it. Now I have three contacts who could be resources in the future if I don't bother them excessively and stay polite and professional, and I haven't spent a penny on anything except an internet connection. Makes me feel really good.
And just so you know, the FBI have a section/office dedicated to answering the queries of writers, authors, film makers and TV scriptwriters! (I know, because I've used their service.)