Couldn't post in Dev's Corner forum so I decided to post this here.
I was able to find this weapon using auction house but it is not in the Mayhem Token Trader. Is this another bug or have all the A&P Series Mayhem BP-20, Perfected been purchased already?
Seems to be a bug, this weapon doesn't actually exist in the game, it's just mistakenly flagged as discovered likely because it was written over an old item ID which was flagged as having been discovered.