Welcome to Mayo Clinic Connect @casscond, I am glad you found this forum, but I am sad you can't find your exact condition. It sounds pretty rare, and there isn't a specific support group for every diagnosis.
Wow! You certainly had a close call it sounds like! And that you had to ask for genetic testing, and were misdiagnosed for several years? Crazy! While we wait to see if another member with your condition pops in here, I assume you have dug in and tried to read everything you can get your hands on, have you read this from the NHI?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5063271/
You mention you are transferring your care to the Mayo Clinic, do you mean Rochester? Have you had your doctor send a referral yet? It can take time to be seen, and the sooner you get in the system the better for you.
I have HCM, and similar to you fell through the cracks in my local town. I was misdiagnosed with five different heart conditions and was finally diagnosed with a rare heart condition, Sub-aortic membrane and told I needed open heart surgery right away. When I ask for a second and third opinion, I did not have Sub-aortic membrane, I had HOCM, and the Mayo Clinic was my final stop. I am so grateful I listened to my inner voice and pushed for referrals. I am a passive person, but I knew I had to be my own advocate.
Do you have confidence in your doctor to ask for a referral to Mayo? Are you able to be active despite your condition?