Maybe corrupted pkg_summary database.
I used pkgin today to install pidgin and only had maybe 20 dependencies.
I use:
$ grep -v ^# /usr/pkg/etc/pkgin/repositories.conf
ftp://ftp.netbsd.org/pub/pkgsrc/packages/NetBSD/i386/5.0/All
(It knows gmome-session too.)
I have:
$ pkgin -v
pkgin 0.3.3 for NetBSD-5.0.2 i386