Adriano,
The IK-3 fihter were used for defence of Belgrade and they did score several kills (IIRC officially 14 kills were credited to the type). If I remember correctly, there is a Serb language book about the IK fighters (but I don't have that book). In English, there was a book about the IK series as well in the '70's (see here:
http://en.wikipedia.org/wiki/Rogozarski_IK-3).
Best to ask the Serb members of this forum.