I'm giving the spades clothe another go. Dark Goblins have been showing up at least once every four times in the place I get them to spawn in, and I have gotten a battle of four.
So far, I still don't have it, but I'm trying so hard to get it. Dark Goblins are just being really picky with the rare item drop rate...
I think the Dark Goblins Rare Item RNG is about 4.70%, but this is just an estimate from hours of battling these guys and them not dropping the rare item.
EDIT: Been farming these guys for about 37 minutes.
I only got an Antenna Power+ from a Dark Dragon and a Full Potion from the Dark Goblins.
Thinking of changing my party so I have more high attack guys on my team with Light Bracelet and Natural clothes so they are able to take down the Dark Goblins more quickly, thus decreasing the amount of time between each battle.
EDIT 2: Game decides to taunt me by getting me more and more Full Potions. Heck, I think I'd have better chances of getting Spades with the AT trick then just by normal means (I would have to use it when I see a Golden Ham and hope that it will call in Dark Goblins like crazy).
A wise man once said, "Absence makes the heart go yonder."
And it's not the other way around.