Where do you get echo dates?

[Leverian]

I saw on the wiki there was a batfolk transformative called "echo dates," but it has no wiki page. Where do you get it?

 

[Ace Hangman]

I know you can get them from batfolk muggers in Undermountain, not sure if it's from the muggers or Nocturna, since she's always with the muggers I fight now.

 

[Kesil]

They can also be found by choice during that "abandonded supplies" undermountain event: