I got those tickets at the AMEX presale last week. I'm not sure how many are available now. And yes, they were available right at the beginning.
Now don't give up in case you can't find them the first time you try. Places like this are notorious for "holding back" certain seats for different sales. Today is another pre-sale (in fact, there are about 5 of them going on right now) and the GENERAL sale is Saturday morning. And even if you can't find anything then, keep trying in the days to come. Sometimes Ticketmaster allows "legal scalping" of seats on Stubhub, Tixchange, etc. If those don't sell they give them back to the venue and Ticketmaster puts them in the general pool. And the show isn't until June. I know it's a roll of the dice whether you'll get these seats in an area you want, but don't give up, keep trying. Anything in the lower - mid arena I would jump on immediately.