Try hockeyfinder.com
The website needs some work, but if you go about 3/4 of the way down the page, there is a section that says "want to play hockey?"
then click underneath it. It will open up another tab where the open hockey is this week. Don't know if they have high school level.
You buy the credits and register for the rink online.
Finding Open Youth Hockey/Rink Rat
Moderators: Mitch Hawker, east hockey, karl(east)