N Reg in Kuala Lumpur
The club that I fly with - Air Adventure has a C172 on the US register which is available to rent. There are others in MY - but often private owners.
There are no FAA Instructors in MY anymore - I knew of 3 but they have either left the country or their ratings have lapsed.
Quite a few N regs in SG. As mentioned above try WingsoverAsia.
I don't know of any in Vietnam (I have tried).
No idea about TH or KH or Laos.
Good Luck