Does anyone know when Season 6 comes out on DVD?

I take it your in America, so I can't tell you that much, being in the UK myself, but at the moment on TV Season 6 is up to episode 13 out of what I guess is going to be 22. The season finae is going to be two episodes back to back, in two hours, and is estimated to air on around the 20th May. Give a few months for a dvd release and you should have it by late summer or September time, would be my best guess.
As for Season 7, we haven't been confirmed to get renewed yet, but let's cross our fingers!! :) If we were to get a Season 7, it would start around September time where you are :)

Hope this helps x

Season 6 will be available sometime in September. There's no official date yet but I know it will be in September. If the show get's renewed for a 7th season the premier episode will air also in September probably a week or so after the DVD releases.