OK, looked at the agents but kept to those that have a good amount of rentals, as many are sales.

The main one in Oliva seems to be Anacasa
Alquiler de apartamentos en Oliva | Apartamentos en Oliva | Inmobiliarias en Oliva

Safor Property Services
Safor Property Services - Properties - Propiedades inmobiliarias: houses - casas, Ronda, flats - pisos, villas, farm houses - fincas, plots - parcelas...

Hamiltons
Costa Blanca Property - Hamiltons of London S.L

and the town tourist web site
Tourist-Oliva.com | Oliva’s tourist information website

Hope this helps