Mariwaka's Bag

I didn't have 2x drop. Took me only 30 minutes to find it.

Don't use the parlor. Use that map with the gunboss in it.

Exactly. I in fact found it by abusing gunboss. During his jumps from the lower platform, you can hit him with a rain/eruption. Continue to do so with as few buff as possible and he will continue to spawn the guys you need to kill to find it. I went through around 4 gunbosses this way and found it within an hour. Granted regular spawn may be just as quick about it, you'd need to get rid of the gunboss first anyway.