I have tried to obtain them with EAC and Plextools but I got the same result: n/a

I have tried with 5 CDs

It is that is not longer used or that not all cds have them? Or maybe my reader is not able to read them?

Feurio CD-Manager -> CD-ROM -> Read UPC & ISRC code
It will appear next to "playing time".

I've just tried EAC now, and ISRC codes don't appear in the cuesheet although EAC shows a window while reading ISRC

Have you checked to make sure the "Retrieve UPC/ISRC" option is checked inside EAC?
EAC -> Tools -> "Retrieve UPC/ISRC codes in CUE sheet generation"

I had read on this board that very few CDs have these (ISRC/UPC)

ISRC and UPC are two very different things.
ISRC is something unique to each track and it's mostly stuff released under larger labels that are ISRC branded.
UPC(-A) is something you call barcode on the CD, and is a 12-digit serie, and often it's an EAN(-13) code which, by name, is 13-digits. this number is either CD-release unique, or just album unique.

edit: Oh, and far from all drives support reading of UPC-A/EAN-13 or ISRC.

Yes, but I don't get any result

I think that my cds doesn't have these codes. I will try to find one that haves them and try to extract them

And thanks for you replies