getting a big box

So...I think I'm in trouble. My contract is up on my apartment on Friday and the box I was relying on using to ship a lot of my stuff in turns out to be a few cm too big.

Looking at the post office they only seem to have really small size boxes as does the supermarket.

Does anyone know of a reliable place where I can get a nice big (the closest to the maximum allowable to post the better) box?

Excuse me, but do you happen to be "walrus" on another thread about package sizes? If so, that 55 by 55 by 55 box fits within the limit.

If you are plannning to ask percel service, you can get boxes from them.
http://www.kuronekoyamato.co.jp/en/send/material/

If you are carrying your goods by youself, go to DIY store such as Tokyu Hands, Cainz Home, Shimachu, Komeri and etc.

I had lost the other the head. I do need another box anyway :p

Visit local drug stores where you can get free cardboard boxes. Ask the staff gently while he/she is not on service that you want cardboard boxes and say "Thank You" three times you will probably get free boxes(toilet papers and tissue boxes are quite large but they are not durable).