Corsair's probably right. It's not like six Hakagas simply popped up a few klicks from the Moon.
I'm pretty sure the cats had a more or less free ride until up to Warsaw, where the fleet was gathering... and then they forced the fleet to pull back 3 or 4 systems until reaching Sol, passing thru Sirius which I believe was a major system at the time too... Not to mention they could've spread out some secondary cruiser and carrier detachments across the entire Vega sector, since Confed was concentrating its defenses on the route to Sol. In fact, Epsilon was also probably left with few defenses, since we know a small Kilrathi fleet got as far as the Landreich systems (then again, I think it's possible they could've moved inside Kilrathi territory until reaching a Kilrathi-Landreich border, if there is such a thing... I don't remember too well).
I believe throughout all those sectors that were either left open wide or abandoned during battle there were at least a few other major shipyards, since we're talking about Vega sector, possibly Epsilon sector, and a part of Sol sector as well.
I think the invaders began to be truly expelled only once other ships started coming online until Confed had enough forces to spread out across all the space they left open in the initial defense effort... although at this point, all Kilrathi fleets combined probably weren't as dangerous as the one which headed for Earth and got it's ass kicked there.
--Eder