Reddit mentions of Arte Shape B2 white SH-B2-WH

next available size is 60x80, and a friend told me that smaller images tend to go down after a bit;

I found some japan-B2 sized frames on amazon.com coming from japan; the guy in this review says:

"This is a very simple aluminum frame that fits Japanese B2-sized posters. The price point is pretty reasonable, though the original product is much cheaper if purchased in Japan. Buyers should keep in mind that Japanese B2 posters (515x728mm) are not the same dimensions as non-Japanese B2 posters (500×707mm)"

No european sellers though

For now the only solution is to order from Leroy-Merlin a custom sized frame

EDIT: I found also this good-priced frames on Rakuten global

EDIT2: this on amazon,co.jp could be more convenient via Tenso