It's a topic that comes up on the forum frequently. Some ARTCCs publish schedules and some don't. But even those that do, you can't hold them to it like it's etched in gold, any more than anyone would try to hold you to a commitment as to when you will be flying. You might give them an idea, or try to fly around the same time every week, but unfortunately few of us can afford to make flight simulation our #1 priority and other things are going to come up last-minute.
That being said, +1 to looking for events to fly during, and +1 to looking for controllers who just recently logged on. Those are my two usual strategies as well. They aren't foolproof, but, they're pretty effective most of the time.