I think the oldest elevators in Thailand are located at Royal Hotel, in Bangkok's Phra Nakhon district. I am not sure if they have been modernized or not, but there are newer elevators installed separately.
For people who don't know what brand of elevator is this.
The oldest one is Edoux Samain Elevator (Ascenseur Edoux Samain), installed since 1946, which is also an innerdoorless one. And additional ones are Mitsubishi elevators with 2nd generation fixtures.
It could have another one older than that, but I just need to research more about this topic.
Video by me: