In my experience with Mohegan Sun it's better to just wait until a month or so before the show to buy tickets. Every big show there "sells out" in 5 minutes because it's a small arena and so many tickets aren't released right away. A huge number are held for the casino high rollers - but the ones they don't take eventually get put on Ticketmaster. I didn't even bother trying to get tickets for these two because I know I'll have better luck later.