Well ... I found tropix on Bocas, they have an email address (thanks for the replies courtney), and page:
http://tropixsurf.tripod.com/
And Radical Surf Shop in Panama city, but I found no information online about them.
So - probably no decent rentals, but maybe I can buy a used board at one of those places.
Also found this diary, including his rental and sale of a board in Panama:
http://www.danger-island.com/~dav/photos/panama/index.shtml
The above is not very surf oriented, but is good for general travelling Panama information.