The Dart Perk is very nice indeed, and I assume the Sharpshooter one is on a similar level of utility. They neatly sidestep the problem of never being able to find ammo. However, it still sucks to be you if you're using a different weapon combination to Sling, Fighter/Bow or Rogue/Darts. There's no reliable source of special ammo unless someone with the perk decides to start selling it. Although White uses a bow mostly, I took the dart perk as it gave me fun things to use at range.
I am aware there are several unreliable sources of ammo, and appreciate the thought that's gone into theming those. However, the lack of reliable supplies leads to "grenade hoarding". You're not certain when you'll really need the badass ammo, so you save it for PVP/DM quests. And half the time, not get around to using it, making things a bit boring. Unlike potions, which you can save up cash for and buy off PCs. It's why I prefer to stock up on Divine Favour potions, they work with ranged weapons and you can usually buy them. The other problem is that there are 2-3 different sorts of Cold/Fire/Acid arrows, none of which stack. It makes it not worth trying to collect them all. I think there's also 2 different item IDs for Bone-Tipped ones. It's the same problem as with potions before homogenisation, but with greater numbers of items as they come in stacks of 3-99 and stack up to 99.
Similarly, what was great with the Arrowhead was that although the +2 Mighty bows were expensive, they were always available. It made playing a shooty PC less of a case of hoping on quest or DM loot to have some reasonable firepower. I got lucky and bought a decent bow early, but it's always a bit of a crapshoot as to what bows are in the economy.
I am impressed by how the Extract Poison Glands tool has solved the same situation for Poison. It's made that a consumable I can proactively go looking for. Could there possibly be a Recover Ammunition tool you could use on dead archers, based on your DEX bonus and if you have Point Blank Shot/Rapid Shot/Weapon Focus for example? Have it recover a stack of ammo from an appropriate loot table. Poison for goblins, poison bolts for kobolds, negative for Undead, Piercing for Bandits etc.
There are ways of at least making very good bullets and arrows without the need for a DM.
However, back in EfU:A there was a shop that sold magic arrows, and it was pretty awesome. Getting something like that back would be great for them.
The suggestion is for adding special ammunitions that are NOT darts, bullets or arrows.
Magic bolts in particular, though dropping occasionally on quests, are otherwise hard to come by.
Yeah, magic bolts in particular are hard as balls to find, and usually in extremely short supply.