For some reason, Swarms are extremely hard to find. Steve said he finds them well enough, however, believe me, or not, I NEVER EVER met a swarm in Aurora C#, and I know a couple of regular players in this forum can say the same.
This was true for me until 2.1.1 - there was a bug that was fixed them that prevented Swarms being generated later in the game, so for us slow-tech conventional start players, we just didn't see them.
Fixed in 2.1.1 and since then I've had a seriously rude awakening... Damn things are murder on a beam-only fleet that can't match their speed
Definitely seem to be generating in decent numbers in my games - I think I've found at least 3 separate Swarms by the time I've hit 150 systems in both my 2.1.1 games, and have been holding border JPs against them and struggling to push them back.