Were to buy Ghibli Museum ticket? Tokyo

Please help!
Were to buy Ghibli Museum ticket?
I try to search to buy online, but need go to travel agent in USA, they asking all full information like we are receiving visa to Japan (passport, all names, full card information and all of this for ticket only, unbelievable!). What is the problem with this Museum.
Question: Can we buy tickets directly when we will arrive to Tokyo in June or can buy earlier 1-2 weeks advance without travel agent?

Your options are explained on the following page:
http://www.japan-guide.com/e/e3041.html

Note that the tickets on June weekdays are not going to sell out, i.e. you can buy them just a day or two in advance at a Lawson convenience store.

This page explains how to use the machine at the Lawson convenience store:
http://www.lawson.co.jp/ghibli/museum/ticket/english.html

You can check out on following site.

http://www.bridge.jpn.com/buy-ghibli-tickets-in-jp

If you can, I would strongly recommend getting tickets from JTB (or other travel agents) or, like me, you might miss out on getting a ticket.

I tried getting tickets at Lawson in September (might be different for June) and all days for 2 weeks were sold out.

I'm going back again this year to tour Hokkaido but allocating a day to go to Tokyo before our flight just so we can go to Ghibli Museum because we missed out last year. This time I am paying the extra 1000yen to secure tickets instead of hoping to get tickets when I'm there. 1000yen is nothing compared to the price of my trip (airfare, accommodation, car hire, etc) so I am happy to pay that knowing I'm guaranteed access on the day I want.

I would get your ticket from JTB. The intimation you give them will be print on the voucher. When you get to the museum, they will match that information with your passport, then you will get your ticket. If you get it from Lawson, you will still have to give the same information in order to get your ticket, which you may have a chance of sold out for the days you will be at Tokyo.

The tour of japanican, ticket seems to be still.
http://www.japanican.com/en/tour/detail/F600_/?typecd=TOU&destcd=M18
Tickets for weekday Lawson, is impossible on that day, but it might buy if before about a week.
If you stay at the hotel, you would be also possible to ask the concierge in advance.