I have read previous posts that mob spawn rates are low which makes it near impossible to get Shadow Gems to progress along the quest lines. I just couldn't find any definite solution. Is it just to beg in chat for people who found a spawner?
Someone let me teleport to where the spawner is located in the overworld. It is at -3398, 88, 107 down in a cave. You can use the /homes and the /sethome command to figure out your coordinates in the world...
There's some in the mob kits, spawners and mobs running around so we never came up with an alternative other than the organic methods above.
Quick follow up.... At spawn, you may want to add a sign that says "You should complete the tutorial stage in Farmworld". That issue comes up like ten times a day...