If you happen to be in Barcelona from the 2nd to 12th of November, you can buy second hand books at the Japanese Library in Barcelona.
The books will be 0,50€ each.
[https://www.google.com/maps/place/Biblioteca+Japonesa+De+Barcelona/@41.3886745,2.1583587,17z/data=!3m1!4b1!4m5!3m4!1s0x12a4a28e592cbae1:0x4491be23d11a4780!8m2!3d41.3886745!4d2.1583587](https://www.google.com/maps/place/Biblioteca+Japonesa+De+Barcelona/@41.3886745,2.1583587,17z/data=!3m1!4b1!4m5!3m4!1s0x12a4a28e592cbae1:0x4491be23d11a4780!8m2!3d41.3886745!4d2.1583587)