Missing source packages in Debian Squeeze repository

Hi all,

Help! On Debian Squeeze, I cannot download any sources for Percona Server 5.1 or 5.5. They appear to be missing.

$ apt-get -V source percona-server-common-5.5
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Ignore unavailable target release 'stable' of package 'percona-server-common-5.5'
E: Unable to find a source package for
$ apt-get -V source percona-server-server-5.5
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Ignore unavailable target release 'stable' of package 'percona-server-server-5.5'
E: Unable to find a source package for
$ apt-get -V source percona-server-client-5.5
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Ignore unavailable target release 'stable' of package 'percona-server-client-5.5'
E: Unable to find a source package for

My system can see the binary packages just fine:

$ apt-get -s -V install percona-server-client-5.5 percona-server-server-5.5
NOTE: This is only a simulation!
      apt-get needs root privileges for real execution.
      Keep also in mind that locking is deactivated,
      so don't depend on the relevance to the real current situation!
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
   libaio1 (0.3.107-7)
   libmysqlclient18 (5.5.11-rel20.2-115.squeeze)
   percona-server-common-5.5 (5.5.11-rel20.2-115.squeeze)
Suggested packages:
   tinyca (0.7.5-3)
The following NEW packages will be installed:
   libaio1 (0.3.107-7)
   libmysqlclient18 (5.5.11-rel20.2-115.squeeze)
   percona-server-client-5.5 (5.5.11-rel20.2-115.squeeze)
   percona-server-common-5.5 (5.5.11-rel20.2-115.squeeze)
   percona-server-server-5.5 (5.5.11-rel20.2-115.squeeze)
0 upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
Inst libaio1 (0.3.107-7 Debian:6.0.1/stable [amd64])
Inst libmysqlclient18 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [amd64])
Inst percona-server-common-5.5 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [all])
Inst percona-server-client-5.5 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [amd64])
Inst percona-server-server-5.5 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [amd64])
Conf libaio1 (0.3.107-7 Debian:6.0.1/stable [amd64])
Conf libmysqlclient18 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [amd64])
Conf percona-server-common-5.5 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [all])
Conf percona-server-client-5.5 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [amd64])
Conf percona-server-server-5.5 (5.5.11-rel20.2-115.squeeze percona:repo.percona.com [amd64])