Yeah, 'O' is usually the hardest to find discounted tickets on...always been that way.
I can't speak for GoldStar, TravelZoo etc., but Best Of Vegas has always had 'em....
If you look at their website, they sell out quick though.
www.bestofvegas.com
I have used these guys a couple times and like 'em...Reason...you know where your
SEC./SEAT will be. Unlike some of the other guys where you take your confirmation
to the box office...THEN you see where you're sitting (and sometimes, it's a pretty poor location)
I've even requested where I sit with BOV. You book with them, they confirm your booking and
then send it in to the box office where your Show is at. In my case w/ Jersey Boys, the sent in
my seating location request too...and I got it.
Finally...a few days later, you'll recieve another email from BOV with your final SEC./SEAT confirmation
which you take to the box office.
They do carry 'O' tickets.