Apply to work as an usher for a venue. Not only can you see your event for free but you could possibly get paid. Venues hire hundreds of people to usher for their events. Sure you may have to work a couple shows you don't want to see, but many of them will allow you to request working inside the venue during the concert or event that you want to see. It doesn't guarantee that you will be able to see your favorite band, but you will have a good chance.
Volunteer for the promoter. Promoter often use volunteers to keep the cost of concerts down. You could be doing anything from load in and load out, to selling merchandise or ushering depending on the venue. Aim for a job that only takes your time before and after the concert and ask the promoter if they offer free tickets to their volunteers.
Keep your ear on the radio. The shots are long, but radio competitions are another great way to get free tickets. Put the radio's number on speed dial and just keep trying.