For one it might be the mission you're looking for. It's called "Support B'Tran Colonization Efforts" or "Support B'Tran Expansion Efforts" (for KDF). I'm just mentioning it, because I know people who have been looking for "Renown" instead of "Support".
Other than that, it's pure luck if it's there or not, if you're not on the 24-hour cooldown. Just make sure to check your OP and visit both Elite and normal, as the doff missions differ between those instances.
Asking in the Doffjobs-channel might help as well, perhaps someone has it on their Ops and can throw you a bridge invite.
Ah, thank you, I'll try both versions of B'tran from here on out. As of late, I did find out it was called Cupport B'tran Colonization Efforts, I just haven't been seeing it. And I've been running the B'tran Doff assignments when they came up just to play it save, save for the one about Klingon attacks, because of the extreme risk level, and the fact it was clearly not it, lol.