He was a miss release with the GUPPS pets, best bet to get him is to post on the advent swap thread.
Also there is an advent help thread to, so if you have any advent related questions you may find them already answered there, and if not one of the moss will answer you pretty quick!
Edit: here is a link to the forum where all event topics are!
I literally didn’t know it existed until two years ago, so I try to share it
https://www.chickensmoothie.com/Forum/viewforum.php?f=108