I was told to do the synth requiring the Lumber Jack key item by an NPC to get experience in woodworking. Right now I am level 44.7 woodworking and I'm working on Horn Arrows. So that means that this synth is at least a lv 45, and I'm guessing higher because the same NPC told me to do Horn Arrows (lv 49 cap) a while back. I talked to the NPC at the drafting table, the one who gives more difficult synth info. Hope this helps someone.

this item is also sold by a little taru near the north gate of Windurst Waters. He's a regional vendor for Sarutabaruta, so his stock is always available and for any quantity (ie: unlimited stock)

i know for sure he also sells Saruta Oranges, Rarab Tails, and Lauan Logs. A good NPC for starting woodworking and people who like OJ.