Just wondering if there are slings or darts in the game. I've made it to Oleg's and in the absence of these items, my druid PC has no ranged attack options.

Besides the sling staff I've Not seen any darts or slings sadly.

And What about cantrips? They are not expendable so if u have a acid splash ar whatever from lvl 0 spells You can put it on your hotkeys bar and select it with right click. It is set as automatic attack then, and will be used automatically when cmbat starts, same way as sling, dart or whatever ;-)

No damage spells are in druid orison selection.

The only way to get darts right now, is to make a character who has weapon focus darts. I made a couple of fighters as npcs, and took their darts for my main character.
Unfortunately 2wep fighting doesn't work with thrown items apparently, so if you use 2 of them you take a -4

200gp for 2 normal darts :p