Scratch

Hmm... perhaps try something like:
[blocks]
<when green flag clicked>
<forever>
<go to[ Sprite that you want to fire from
<turn cw( <pick random( -10 )to( 10 )degrees>
<repeat until><touching color[ colour of sprite (make sure the stage has a border of this colour)
<move( 5 )steps> This can be changed to speed up/slow down the missile
<end>
<end>
[/blocks]
Hope this helps!    Also, I'm moving this to "All About Scratch" - just to let you know how it got here