I had the hardest time finding a new helmet last year. I didn’t have the budget for a Charles Owen or a GPA, and had almost given up hope, but luckily I discovered Tipperary helmets! Not only do they fit, they actually look good on me!
I wore an adult medium/large as a 9-year-old and my head has only grown since! I don’t even know what shape my head is, I just know that I tried on 5,000 of everyone else’s favorite helmets before I found one that even remotely fit.
Good luck with your search!