Looking for travel company for Colombia's archaeological sites

I've just returned from an OAT trip to Colombia which was a good experience. I'd like to return to visit the archaeological sites of San Agustin (in the south which has numerous megaliths) ; La Cuided Perdida (near Santa Marta; which has ancient villages - though I understand this can be a difficult trek); Tierradentro (in the Cauca region - which is known for its underground tombs) and Villa de Layva (4 hrs. from Bogota which is known for lots of fossils). Does anyone know of a good company, preferably in Colombia, that can arrange a custom tour concentrating on the archaeological sites? Thank you for your help.