Sorry about the late reply to this, been a bit busy today is all :P
The three items you need for the acid should be located in the three sections that split off from the map you find out about needing the acid. Other than the direction you came from, there should be a map to the left, another in the top right and one last one at the bottom right. Since I don't know which of those you've already checked out for the first two parts I'm not sure which one you need to visit to find the last part, but you should be able to find the dryad that's holding the last piece in whichever of those areas you've not explored yet. :)