Wait, I think I got it. Someone correct me If I'm wrong, but I think that I should have ( I added comments to explain what I believe each line would be for, maybe to help a VCE noob that's reading this)
1. OnActivate > player > VCEifVariable > pistol > less than > 1 > [1 2] (for checking if you already have a pistol.)
2. OnvariableTrue > Client > VCEifVariable > kills>greater than or equal to> 5> [3 6] (checks if you have enough kills.)
3. OnvariableFalse > Client > CenterPrint > You can't take 2 pistol types. (tells you that you took a pistol already.)
4. OnvariableTrue > Client > CenterPrint > You took a pistol. (tells you that you got a pistol.)
5. OnvariableTrue > Player > VCEmodVariable > pistol > set > 1 (goes with the check in the first event, activated if the kill check turns up true.)
6. OnvariableTrue > Player > Additem > Pistol (gives you the pistol, obviously)
7. OnvariableFalse > Client > CenterPrint > You don't have enough kills. (Activated if the kill check turns up false)
Please tell me If this wouldn't work, I tried testing it by making bricks that set the kills to different numbers of kills. Seemed to work fine.