I'd recommend going to
http://www.sportsbookreview.com (independant review site).. check out the top10 and their programs for affiliates.. based on that you already know that you are selling a great product and since most of these kinds of sponsors pay %, you can get recurrings year after year...
Would also recommend using some geo-tools to give different ads for different areas. For instance, nobody in the scandic countries would use a us/caribian bookie, nobody in the us would use a nordic bookie etc. A different approach would be to push sportsbetting exchanges that sends people to different areas based on geo... (for instance betfair.com)