Ghibli musuem tickets in summer break?

Hi, I'm visiting some Japanese friends over summer break and I kind of promised them I would buy them Ghibli museum tickets as a thank you for letting me stay at their place.

Aaand then I found out that you can only buy tickets for Japanese residents at Lawson so I'm planning to just get them when I arrive in Tokyo. I'll be staying there from July 20 till August 5 and I've been given the impression that that's when all the schools in Japan have summer break as well.

So my question, are the chances big that the tickets are sold out when I arrive because of the break? Or should I be okay?

I've found this site to check the availability of the tickets
http://l-tike.com/ghibli/
but even though my Japanese is decent I don't really get it. I can get to the calender part but then I don't really understand how to see whether tickets are still available or not. So if someone could explain that to me I'd be grateful :D

Thanks!

You reached the calendar for June? (Tickets for July become available only from June 10th)

The time slots and dates where you see "x" are sold out. Only those with "circles" are available.

Hi Suus.

I heard that if you wait until you arrive, tickets usually are sold out already. To avoid that I used www.govoyagin.com to pre-order tickets when I visited last time. It's a bit more expensive than Lawson, but it guaranteed I could get in! that's all I cared about :)

Why not book a tour with a travel agent?