I spent quite a long time farming these in Batallia Downs trying to get fruit seeds, but no luck so far and that was a lightsday... maybe I should try it in a darksday, but anyways not good if you're looking for fruit seeds.
I'm gonna try caveberries and then Ordelles Cave, but it seems the fastest way to get these is buying them in Jeuno or logging.
T_T gardening is great,but its a lot of work.