ok, Shark Helmets are distributed in the US by Tucker Rockey distributors. I did a search from my zip code and only three places came up that were TR distributors and could get the shark. The nearest two were either indy superbikes or bloomington power sports. Here's the link..
POWERSPORTRIDER DEALER LOCATOR RESULTS

You might call the guys at indy superbikes and just let them know you're concerned with the whole size issue and ask them what their return policy would be should you order it and it not fit.