the thing is, not all dealers hold all helmets...
go to every dealer you can find and try them ALL on... forget what they look like...
i wear a XS AGV, a Small HJC, and i tried on an HJC symaxII which was medium, and the scorpion 1000 was a large.
most important thing of all... find one that fits your noggin...
search all the stores...
then when you find one that fits... look online for a better deal
check this page for useful info... we all have different shape and sizes of head...
Motorcycle Helmet FAQ - webBikeWorld