For me personally, I try to take a multi-faceted approach.  I typically will conduct pretty exhaustive research online (using authority sites, trade/industry publications/etc), so that I feel like I at least have some working knowledge about the topic.  From there, I can then come up with an exhaustive list of questions.

I will then check with people in my own personal network, and if I don't know someone personally with expertise in the subject matter I need advice about, I will ask for referrals.  If that comes up empty, I'll head back to Google and try to identify industry experts.  Once I've done so, I immediately head over to LinkedIn to see if someone in my network is connected with them.  If so, I'll reach about to see if they are comfortable doing an introduction.  If not, then I'll try to "cold outreach" approach.

Since I've done research on my own, and have a bunch of questions already put together, these conversations end up being a lot more meaningful than if I were to just go into things blind.  

In certain instances, I will also talk to other business owners that I know through various business masterminds I'm a part of.  Since these people are typically in the same industry I am, what I've found is that some will have dealt with similar issues... and can be a wealth of information.

Hope this helps!