If you're using OpenSA2, you have to look in the Articles section, since you're dealing with hitboxes attached to props.
If you're using PSA, you have to enter a number into the Offset box in the Sub Routines tab to find what you're looking for. Lucky for you I'm feeling generous enough to tell you what those numbers are.
Homing missile: 168F8
Super Missile: 169C8
Bomb collision: 17918
Bomb explosion: 17A78
Note that PSA doesn't recognize that special hitboxes have two extra parameters, so you'll have to use OpenSA2 if you want to change things like rehit rate or reflectability. Also, the graphic effects (aside from the impact effects) are stored in a different place; I don't know where they are right now.