Id approach experts in the field, tell them what your working on in a sentence or two and see if they will help with a quick call/email. Have a few q's prepared, dont waste their time. People genuinly interested in helping further will let you know, or can put you in touch with someone who can (eg a great junior they know).
Some general tips
- Good founders will always try and pay it forward, even the big (locally) famous ones
- Check out trade associations, they are typically open and can hook you up with an expert.
- Avoid VCs & other people who are busy or only tangentially related to the industry
- Avoid people who are very publicly associated with an industry (usually just personal-brand folks and busy)
- Look for people who have been execs but are now semi-retired (commissioners etc)
You can use a simple template like this
"Hi xx, im building yy to do zz. I was wondering if I can send you some questions to learn from you?"
I did this before and a lot of nice people gave me time, some v big names in the field (to me, a randomer). Just come prepared, keep it short, be thankful, dont try sell them your product etc.
Edit to add: I used linkedin and email to contact.