I am in the same boat (ship) I went from CA to VA in a short time using only DOFFs. I think that you must complete a few of the missions in order to unlock that mission. I was looking for a list when I saw your post. I am thinking it may just be a few of the first contact missions that opens up a new set. I will let you know ASAP.
Because of the forced linear mission progression now you have to complete or click skip on every mission that comes before the mission that has you go b'tran. It won't even show up until you have either completed or skip the other missions.