I am at the Hidden Forest story arch. I grew a lot of Willow trees to chop now, so that I could take the chance and get some forest vines from them. But it seems that the Willow trees have stopped dropping forest vines. @PikaSquirrel, would this be a mission for you? :-) Thanks in advance!
I just got a forest vine, so, no case here! I must have caught my Willows in a drought at first. :-)