It strikes me as odd that NPC monsters of certain types have these in a nigh unlimited supply, but to players they range from uncommon to prohibitively expensive due to the rate at which a dedicated ranged character will burn through them.
So, why not have NPC monsters equipped with these drop a fair amount with a fairly high chance of doing so?
Let's say, 20-30 arrows with a 70%-100 chance of dropping?
In my experience I have never really had a problem getting 'special' arrows/bolts/stones. While they usually drop in small stacks, nobody but archers go for them after quests and buying them off of players is usually very cheap.
Just an opinion.