I'd add: make it super clear that you are not going to asking them for a job or a referral or selling them anything during the conversation. That will increase the likelihood they'll take the call.

If you can get a warm intro to them, all the better.

I'd also suggest expecting people to say no, and not taking it personally. If you ask enough people, you will find some that are happy to spend time with you, but it won't be everyone. If you do achieve your goals, some of those people who say "No" might be future co-workers.

So just ask, accept whatever you get, and keep asking more people.