Try to call ahead for hotel reservations in the rainy season. The risk is not so much that places will fill up as that business may be so slow the manager may not even be around to check guests in.
Most of the places listed here are in Pedasí [1], but there are a few others either on or near the beach. Three of the nicest accommodations are near Playa Destiladeros [2], south of town.
Links:
[1] http://www.moon.com/destinations/panama/the-azuero-peninsula/pedasi
[2] http://www.moon.com/destinations/panama/the-azuero-peninsula/pedasi/sights/nearby-beaches