That's a tough one, I checked in the Tico Times guide book, but they only have a few companies that offer the whole tour.
Since you listed Atenas I thought you might try contacting Bi Costa Rica Bike Tours for ideas:
Kevin Hill
Cellular phone:
011+ 506 380-3844 (Service is poor),
Home: 011+ 506 446-7585 Fax: 011+ 506 446-7585
Mail:
bicostarica@bruncas.com Good Luck!