check out Shooting Sports USA - there are match listings in the back - http://www.nxtbook.com/nxtbooks/nra/ssusa_201204/
You can sign up for a free online subscription here - http://www.nrapublications.org/ssusa/
And I'll second the advice to just start going to matches, shoot what you have, and let your experience and the advice of other shooters guide you. BE shooters tend to be very good about helping out new competitors. Also you can often find some great deals on used guns and gear, so it's worthwhile to hold off on buying too much until you get acquainted w/ the sport.