Keep slogging! Seriously, it ain't easy. Clubs use booking agents for the same reason landlords use real estate agents - to screen out the 'riff-raff'. Put a comprehensive press pack together - including a DVD and CD, photos of your band in action and links to your online videos and music, FB page, etc. and keep sending them to the agents. Most will look at your online link for less than a minute to make a quick judgement on whether you deserve any further attention, so make sure you've got your best stuff ready.
My reverbnation site: http://www.reverbnation.com/mikebirchmusic
Youtube: http://www.youtube.com/mikebirchmusic
Facebook: http://www.facebook.com/mikebirchmusic
Youtube: http://www.youtube.com/mikebirchmusic
Facebook: http://www.facebook.com/mikebirchmusic