I'm not so sure this needs to be moved. At a quick glance, I don't see anything in the raws reffering to quivers, or what they can hold. Perhaps, in the same way that ranged weapons can be told to use certain types of ammo, there should be such an option with ammo containers? Either that, or all ammo should be placeable within a quiver. If the first, then all those who make new ammo types, and dislike placing everything in a quiver, could have separate ammo containers made. For ammo, it could be some sort of pouch rather than a quiver, or depending on the gun, it could be magazines. I know not everyone approves of guns, so maybe spears/such could be designated to be thrown, or rather have javelin added. Those probably wouldn't go in a quiver, so it could be used for that as well. A'course, then we'd need a way to have a dwarven hand designated as a ranged weapon that uses thrown items... actually, that's not a bad idea either... Or someone could mod in a ranged weapon called a dwarven hand, but then you might see Urist McThrower wielding a +horse leather dwarven hand+ or something.
Ok, got a lil' out of hand there, but still, moddable ammo containers would be a good thing to have, if they don't already exist. And why not have dwarven throwers put in, and specify what should be thrown, eh? Maybe even have units able to be designated as throwable...
new way to rid of cats! Oh wait, you can already throw units, now just make such a move accessible to fortress dwarves rather than just adventurers!