Help: cannot download covers

[mbarmbar]

Hi all,
While I successfully retrieve metadata of my books, and I always see the "Has cover" flag enabled, 90% of the times I cannot download the cover, receiving this message:

calibre, version 0.7.56
ERROR: Cannot fetch cover: ...
openlibrary.org covers: ISBN: 9788838923340 not found
amazon.com covers: No cover found for ISBN: 9788838923340

Running Calibre in debug mode adds confusion, in fact I have:

openlibrary.org covers: HTTP Error 404: Not Found
amazon.com covers: cover for 9788838923340 found
amazon.com covers: cover for 9788838923340 found

Any idea? Is it possible to change somewhere amazon.com with amazon.it? (I'm Italian, reading tons of Italian books).

Thanks in advance.