However, it disturbs me that Win32::Lanman, though powerful and comprehensive, is not on CPAN. Anyone know why?

It's there, the source package just doesn't contain the data that CPAN needs in order to index it. You can find it in the authors/id/J/JH/JHELBERG/ directory though. Maybe someone needs to reach out to the author and create at least a META.yml file for them to include that would let it get indexed.