You can find flights through Momondo.com
Some airline companies flying from Europe:
– KLM: Amsterdam – direct to San José or through Panama.
– Air France: from Paris direct to San José or through Panama.
– Lufthansa: from Frankfurt to Panama with connecting flight to Costa Rica. In 2018 Lufthansa will start a direct flight to San José.
– Swiss Air: Direct from Zürich.
– Iberia: from Amsterdam, Brussels or Düsseldorf to Madrid, with a connecting flight to San José.
Besides the better known websites you can also look for flights at: Google Flights
Costa Rica has two airports: Juan Santamaria I.A. at San José (SJO) and Liberia (LIR).