Any charger capable of 4S or greater operation will charge two packs, it just depends on how much soldering you want to do.
Bear in mind that many chargers will do 6S, but the current that they'll put out will be significantly lowered, as they will probably only have a low power rating (~50W).
Better choices would be:
A FusionRC L120 Pro. Capable of 12S charging, with 180W, this'll charge your packs with no problem. In fact, you could charge up to 6 2S packs on there at once (though the wiring would be messy). As it uses two balance boards, all you'd need is an adapter lead for the main power leads - easy enough.
A Hyperion EOS0615I DUO III. This has two completely individual charging ports, each capable of 6S and 15A. They have a 180W limit EACH!
An iCharger 106B+. This is probably the best bet for what you need it to do for the money. The iCharger's balance boards are ready to accept more than one balance connector, so all you need to do is make a series lead up for the batteries' main leads. This is capable of 6S and 10A, but most importantly, of 250W max of charging power. Your charging time won't be affected by the voltage, unlike on many cheaper chargers. I have the 'big brother' of this charger (the 208B that JonyNitro linked to) and it is very simple to use, effective and the firmware can be updated on the computer.