None of the MTM shirts I have ever bought have had shanked buttons.
are there any online MTM places offering this feature?
I haven't seen any in my browsing.
There are machines that do shanking too. I have seen 2 types:
1. It uses a special thermal thread. The thread is wound around the shank part and then a heated metal piece presses against the thread, sealing it. This shanking would not generally come off on its own.
2. The older, more common machine uses an ordinary thread, which is would around the thread below the button. This shank tends to come off after a few washes.
On Luxire shirts, we attach the button using a machine. It is then shanked by hand in a manner that strengthens the button attachment and also the shank remains reliable.