There is a Caravan operator based in Hanoi Noi Bai called Hai Au Aviation. They fly tourists to Halong Bay and I mostly hear American accents on their transmissions.
Also, there used to be a Caravan operation between Hua Hin (Gulf of Thailand) and Rayong (opposite side of the Gulf, next to Pattaya Sin City), sometimes you could spot them in Bangkok Don Mueang.