Try,
$ sudo ./cross-get linux-kernel-headers arm stable
http://ftp.uk.debian.org/debianpool/main/l/linux-kernel-headers/linux-kernel-headers_2.5.999-test7-bk-17_arm.deb :
05:16:20 ERROR 404: Not Found.
Note debianpool instead debian/pool and : at the end of package name. :-/
Note also that doing that stamp trick to update apt-cross database, if you want a new database, you have to erase time stamp file, in other ways it does not work.
Regards,
Hector Oron