Walindi Plantation Resort and MV FeBrina recommend the following Spanish agencies, listed in no particular order.  The country code for Spain is +34.

Ultima Frontera 
Contact: Ramiro .. 
C/- Francisco Gervas,  17 7oH,  28020   Madrid 
Tel: + 34 91 571 8470 / Toll Free:  

The reefs are pristine and offer what I assume is diving as it was 100 years ago. The bonus was Orcas on the last day, something that I will not soon forget.

Travellin-Tireman, Canada (Trip Advisor - June 2014)