i've seen the STF missions pop up from time to time, think i've still got one active in my 'log' somewhere that i haven't dropped actually... says a min of 5 people recomended though
Ah, that could be Terradome, the only old school STF left in the game.
It is a fun mission that features the Undine.
The other 3, featuring the Borg, are split between ground and space episodes and only accessible through the PvE queue system. Same as the fleet actions, another type of group content.