Mauna Kea is 4,207m above sea level and can definitely see the oceanic horizon. Mount Wilhelm (4509m) and Puncak Jaya (4884m) are the highest peaks in the central mountain range on the island of New Guinea, which makes the ocean horizon probably visible from those peaks.
Western peaks in the Andes are perhaps 150-200km from the sea. A tall peak in that portion could probably see the ocean. Chimborazo (6263m) is ~215km from the sea as the crow flies, although there is a large valley ~100m above sea level in the way.
That looks like a good place to start. It's got a 4205 m peak, which would give 231.6 km to the horizon.
Next place to look is probably at Puncak Jaya in New Guinea, which is 4884 m, giving 249.7 km to the horizon. But there is enough other land in the general vicinity of New Guinea that there could be over-the-horizon peaks visible, so it would take some work to check.
