You can go the gardening route and plant Goose trees. It isn't guaranteed that they will drop it as their harvest though. About Gladiator Dimachaerus, he is a pretty hard boss. So ask a high level friend to help you out in case he is too over powered for your level to handle. To get to him you need to go into the dungeon Mount Olympus in Aquila. You need to find Eris Golden Apple, Then just go straight ahead, past the statues. It is called the Pit of the Noxii.
I hope this helped. I really couldn't 'describe' the location of Gladiator Dimachaerus. Sorry about that, but I tried my best.
wizard