Most events are independently operated. US Lacrosse set guidelines that fit the events that they run. Not every team plays in their events, so identification cards issued from US Lax with D.O.B and current grade would be the best answer. It will give proof that can be used at any event. Should not be that hard, they could have an option to upload a picture during the registration process. When it comes in the mail you have the id card ready to go.