There isn't any taxi-brousse coming here, but you still can find vehicules from Tsiombe when it's market day, or if you're lucky. Just ask there and if there is something everybody will know. During the lobsters season, pickups drive along the coast to collect the lobsters. You can have a lift with them.
If you're not lucky, hire a zebus cart, but be prepared for a long trip. Zebus don't break speed limitations, they tend to go at about the same pace than you - so 4-5 km/h.
You also can walk the 30 km from Tsiombe.