I do not believe there are any off-the-shelf solutions to add these to an existing garage door opener. The pieces are in place; including:
a. Smart Buttons such as the ZRC-90 and the Aeon Aeotech (both available on Amazon). These have native or community developed Device Handlers.
b. Smart Garage Door opener such as the NuTone or Linear (available on Amazon). These have native (SmartThings supported) device handlers).
c. A Smart App that creates a multi-button device as a pin pad (“Use Buttons As PIN Input (“Security Keypad”) e.g., Aeon Aeotec Minimote, ZWN-SC7 Enerwave 7 Button; trigger to Routines, lock/unlock, arm/disarm, mode, lights”. Fairly old, not sure if it still works.
The cost is around US150 for the components and the effort is to update the SmartApp to communicate with the Garage Door Device Handler. You may only have one PIN available; however, you would be able to change at any time and (with your phone) open/close the door at any time.
Perhaps someone has an off-the-shelf solution to your challenge.