Assuming you'll be in Panama
City - Best to go to the Amador Causeway anchorage with a VHF
and get on Ch 74 at 8am with the local cruisers net, then give your qualifications ....many are looking for (unpaid) line-handler's help. And, on Thursday evenings go to the cruisers pizza night held next to the Amador anchorage and meet some of the cruisers in person. Lots of info on the morning cruiser's net for you.
FYI- Most Captain's will pay your return fare back to Panama City.
Option #2 (much harder) If you're on the Colon side, go to Shelter Bay Marina and walk the docks, ask around, have a couple beer's in the restaurant, and/or leave your info on the cruiser's board inside by the main office. Be warned, it's an expensive cab ride (each way) from Colon to Shelter Bay and it's NOT a cheap/easy trip either way as there are NO Taxi's at Shelter Bay Marina, and I would not advise you to stay in Colon. Best to do your search from the Panama City side. FYI- it's an $80 cab fare one-way
from Shelter Bay to Panama City. You can hire a local taxi by the hour/day...work the best fare, or ask the local cruisers for a good cabbie's phone
number who speaks English
if you need...they DO KNOW who is best.
And, I'm sure others will have more great ideas for you as well.