NEVER GIVE UP!
(google search of va.gov)
To find a doctor who can provide a nexus letter with expertise backed by studies, research, and journals, you should seek out a licensed specialist or independent medical examiner (IME) who has experience with VA claims and medical literature research.
The doctor should be a specialist (e.g., orthopedic surgeon, neurologist, pulmonologist, or psychiatrist) in the specific field related to your condition. Their expertise lends more authority to the opinion in the eyes of the VA.
The medical professional should be familiar with the VA's requirements, including using specific language like "at least as likely as not" (a 50% probability or greater) when linking your condition to your service.
A strong nexus letter must cite specific medical literature, studies, or peer-reviewed journals that support the physician's conclusion.
The physician must assert that they have thoroughly reviewed all relevant medical and service records, including your VA claims file (C-file).
Look for doctors with board certifications and solid professional reputations, as the VA often assigns greater probative value to their opinions.