They actually aren't as rare as you may think, not to say they are common though. the key is being in the right place at the right time.
There are many place where characters "appear" at certain times. I call these places "
prankster spots". I'll provide a list of places where they occur, but first, it is important to realize that you have to be near the spot, but not on top of it, and also that these spots are active at critical times such as 11:30 A.M. 3:00 P.M. and any other time a bell rings, or something "critical happens" Also, the pranksters will not always be carrying a Volcano 4000, it could be a kick-me sign, rat, stink bomb, etc.
-outside the motel, usually a Bully appears with a "prank" (all times of day, except night)
-outside the dorm near the hole in fence (at 11:30 and 3:00)
-near the library where the tag spot is (11:30 and 3:00)
-in the parking lot where Russell stands (11:30 and 3:00)
these are just a few examples, there are other spots, but you'll eventually find them.