If you are willing and able to travel to the US, Dr. Reinish and Dr. Levitin are great options. Dr. Waner travels to Berlin a few times a year so you might also want to investigate that option.
Not sure why doctors in the UK and Canada have different opinions about treating birthmarks. Many doctors in the US are similarly resistant to treatment. I think it is because they are not educated with the most up-to-date information on the treatment of vascular birthmarks-so much can be done! I also think that in Canada and the UK, the health system plays a huge role - why treat a "superficial" birthmark that will "go away" when there are so many other people needing "non-cosmetic" care.
Good luck in your search!