See if our site sponsors, Suttos, have them, there is a link to them at the top of each page.
Here is a tip,you best make sure of the fit for the boys ones and don’t go buying one that they will “grow into”, My son wore mine one day and it was a bit big and every time his helmet touched it ,the brace would ride back a little,untill it was all but choking him and he could no longer look down. That was only after one lap of the MX track.