If you enter the Matsumoto Castle, why don’t you drop at the souvenir shop in the castle garden?
It is located in the right-hand side after the ticket booth to enter the castle garden.

A Matsumoto citizen’s group made a new souvenir and has begun to sell since February — two kinds of stickers.
They are mainly targeted for foreign visitors. One is designed Matsumoto’s traditional folk craft, temari balls.

If you put it on your suitcase, you can easily distinguish it from others.

In the shop, there are many other souvenirs, such as armor helmets, T-shirts, temari balls, key holders, smartphone strapps, etc, etc.