Just found it in the betazed sector

I went to the Bavar System (in Alpha Quadrant) where an Espionage mission popped up: "Investigate Illegal Gambling"

As soon as I accepted that mission the "Bribe Ferasan over information about Jem'Hadar in the sector (5/10)" popped up in my mission log.

I did this with 4 characters on a row (before sector reset), and it happend with each and everyone of them.

Happy days; after 4000+ hours ingame I finally managed to continue this quest chain.