I have the same problem. My current solutions that I'm still working on completing (some of which I'm sure aren't viable for you) are as follows:
Googling "ADHD Specialist in _______", looking to see who appears most qualified, then calling to at minimum leave a message to speak with them.
Speaking to the counseling center at my university
Speaking to other friends who are ADHD / on my meds as well.
I'm starting to think that my GP won't cut it anymore for what I'm looking for, I want someone who can answer specific ADHD med questions without referencing something and getting back to me. I want someone who says "haha yea I spoke to a man last year that said the exact same thing! Here's how I was able to help him ..... want to try that?" I think a LMHC with a specialization in ADHD is what I've zeroed in on... try that... I'll let you know how my quest turns out if it's worth it