I would suggest looking at endos in lb, they have gath, and some boneheads in stock, or can at least track something down for you. you may wanna ask around plenty of people have old kids gear, i sold all of mine about 5 years ago that was only used a season or 2 when i was younger then sat for 8 years untouched
My daughter, now just 12, has used a Gath for the past two seasons. What she likes about it is it's so light, lighter than anything else she tried. We bought direct from Gath in Australia and helpfully they fitted extra padding to make the helmet smaller to her measurements.
I still have The helmet I used then we first started racing, they could use that if you want. But If you were looking for a new helmet. Here is the link, for Bonehead helmets, I have one and really like it.