Easy enough to arrange and pretty common, but hanging out waiting for schedules to sync up can get spendy.
Both the Balboa
Yacht Club (pacific side) and Shelter Bay Marina (AKA "Shelter Pay", on the Atlantic side) have boards full of line handler postings and bars to hang out in and meet other cruisers.
As the time gets closer you should also try the cruisers nets, like SW Carib or Pana Connection, both SSB
nets on the Atlantic side (though occassional Pacific traffic pops in to say hi).
Ive been invited to line handle a few times without even deliberately looking...just hanging out working on the boat.
Taking the train is an interesting way to get back and forth if it fits the schedule.
is really making visible progress. New locks at Gatun are flooded now, but not yet in operation.