Nathan, chsjewel7770 gives us great information, I was unaware of the upright MRI of the brain. You might have a struggle finding a provider both of the requisition and of the scan. In your position I would call neurolaunch. They will know where the scanners are located and they'll know which neurologists are prescribing. I would also contact chsjewel and ask for the name of her prescribing neurologist. https://neurolaunch.com/contact-us/
This would be the first test I'd pursue most aggressively. But I wouldn't wait for the upright MRI of the cervical neck because you can seek them at the same time. I suspect the brain MRI will take the longest to secure. Both of these scans are preferrable to the lumbar puncture scan that I suggested because they are noninvasive. So I would leave that scan until there are results from the other two. And keep posting because every time you post a new person will see your questions. Bless your struggle