you could try through your school or college? i know here in New Zealand all the secondary schools have competitions and then there is the winter Uni games which has boarder X, these types of events will let anyone enter.
or you could simply try asking up the mountain and the information office or in some of the local ski/snowboard shops which might sponsor a local event.
I dont know your area so cant give you specific advice but this should give ya a general idea. Just look for any open competitions.