Ghibli tickets go on sale 10th of each month.
If you want to avoid the scrum, we recommend you check out the option to purchase your tickets through a personal shopper on Fiver.com
Please note tickets do sell out quickly.
Studio Ghibli Museum near Tokyo
International ticket sales for the Studio Ghibli Museum in Tokyo go on sale on 10th of each month at 10am Japan time for visits the following month.
Here is the link for the direct purchase Ghibli Museum tickets. https://www.ghibli-museum.jp/en/tickets/
Ghibli Theme Park near Nagoya
International ticket sales for the Ghibli Theme Park (specifically only for the Ghibli's Grand Warehouse section of the park) near Nagoya go on sale on 10th of each month at 2pm Japan time for visits 3 months later. Ie June purchases are for September visitis, July purchase is for October visit, August purchase for November visit and so on.
Here is the link for the direct purchase of Ghibli Theme Park tickets. https://ghibli-park.jp/en/ticket/