You should not be discriminated against for Parkinsons by travel insurers, unless you have difficulty swallowing, or are prone to falls, which is unlikely with such a recent possible diagnosis of maybe P.
These are the 2 questions that we are asked when we renew our travel insurance every year.
Just the same for motor insurance as long as you have disclosed this to the DVLA your premium should not be affected.
Maybe the problem is that it may not be P, but another similar condition, and that is why, until you get a definite diagnosis, it will not be possible to insure you. Perhaps the neurologist could help by saying that is is probably Parkinsons.
May I ask why you have not been diagnosed yet? If it is because you are awaiting tests then that is another reason for insurance being declined.