I have seen all sorts of k'nex grenades. and i think at least one launcher but they aren't really universal.
What makes my launcher unique is that it fires almost any knex grenade.
Step 1: The Base
To build the base you will need:
-5 blue rods
-1 blue+grey double clip.
-2 yellow rods
-1 grey rod
-1 black end clip
-2 grey clips
assemble it by looking at the picture bellow. It's very simple.