I recently had some issues unlocking the Kalmer-1 Tranquilizer as well. For me, I found the problem is that the Mission Story “Breadcrumb Trail” is bugged.
To unlock, the challenge wants you to discover 3 specific clues: the lawsuit documents, the videotape, and the photo in Janus’s basement. However, if while doing the Mission Story, you pick up any additional clues - the letter from Janus on the bodyguard, the microfilm, etc. - it disrupts the Mission Story because 3 clues are discovered. The Mission Story reads as completed, but the challenge connected to the Mission story doesn’t unlock until you pick up those 3 specific clues.
On my last run, I actively avoided picking up any other clues and was directed to infiltrate Janus’s house after listening to the video tape. But on previous runs, I picked up the letter or the microfilm, and then the Mission Story ended right after listening to the video tape. Doing it that last way unlocked the final Mission Story challenge and I finally got my tranquilizer gun!