Actually, my bad. since the dart is a weapon featured in the PHB (no, really!) we don't need to include all of that info. I'll let the attack line speak to how many can be fired as a full-attack. I want to put how the gas affects targets back the way it was in RoF.
Stun Dart (Ex): A bozorg may fire a number of hollow darts that release a small puff of poison gas upon hitting a target. The victim must succeed on a DC X Fortitude save or be stunned for one round. After one round, the target must succeed on a DC X Fortitude save or be stunned for an additional 1d4 rounds. A bozorg carries X darts before it must be reloaded. A bozorg can fire other varieties of darts appropriate for its size.
Do we keep the DC at 12? Maybe so, because these are manufactured weapons? Of course, the 12-HD variety will be fighting foes who will almost never fail their saves...
I don't see why firing other types of darts would be a problem, so we can leave that last line in there.
As for how many darts it can carry, that should be a function of size. Maybe enough for them to fire at, say, 5 or 10 rounds using a full attack?