I forgot to add that I have all the tbz2 tarball with the sources files. I
made a little script to populate /var/db/pkg/cat/pkg, remain the specific
files related to each pkg.

I'm thinking of using ebuild helper with a little script which could
decompress the tbz2 to D and then make ebuild merge  again. I have the
portage tree of the lost db/pkg. So it's doable.