select VOLUME_NAME from LIBVOLUMES where volume_name not in (select volume_name from volumes) and status='Private' and last_use is NULL and owner='
If your library uses different types of media (LTO-2 and LTO-3) and you have different volume label series for them you can add another filter to further refine the results. For example my LTO-3 tape labels all start with L3 so I use:
select VOLUME_NAME from LIBVOLUMES where volume_name not in (select volume_name from volumes) and status='Private' and last_use is NULL and owner='
Once TSM has generated a list you can then run it through a while loop to reset their status or do further refining of the list if you like. If you are proficient with scripts you can automate the whole process and make life a lot easier.