As the GM is there a way to directly contact people who are registered for my events? 

No, we don't give out player information such as email to GMs. The best way to do that is to put in your message to registered players something requesting that players contact you pre show, but you still should be prepared, because that some players will not do that.

If there is critical information that you must provide players, and omitted in your event description, you can email events@gencon.com and request that they pass the information along to your players, but we do have to do that manually, and it is time consuming, so we ask that you only request that should it be critical to the running of your events.

Marian McBrine
Event Coordinator
Gen Con LLC

Thanks Marian! I was 98% sure there wasn't a way, I just wanted to make sure I hadn't missed something :)