Goku never used Spiritbomb during SSJ
That's a fact
the reason:
I hope you guy know the scenes I'll count...
With his first spiritbomb (against Vegeta) he said that only guys with a good heart can control a spiritbomb ...
You know the reason for being a SSJ ???
"You" can only go SSJ when your heart is pure and you're REALLY angry ... If you're angry your heart can't be good ... And that means that you can't control a spiritbomb ...
If you don't trust me, look DBZ Movie 7 ... there they say (nearly) exactly what I said ...
(One more in this movie: Goku made a spiritbomb a THEN went SSJ ... Then he absorbed it and got "really" a bit stronger (noone knew we he'd that, but it happend))