Em... We can make it only HIT 3 times... if that's what you're trying to refer to. Making it "Stop" spamming after 3 hits is impossible I believe... Not sure how the source would be able to detect that.
But, if you want it to only hit 3 times, look for it in your skill_db.txt
136,-1,8,1,-1,0,0,10,8,no,0,0,0,weapon,0, AS_SONICBLOW,Sonic Blow
Currently hits 8 times.