Once you exceed the capabilities of the A4988 driver boards and similar products you move into the realm of commercial stepper drivers and hgher prices. There are many to choose from. Google 3A stepper driver or 5A stepper driver. If you need to drive a few motors there appear to be boards available that can drive 4 motors which appear to be better value.
Most of them take the same inputs as the A4988 - step direction and enable and should work with the same code.
...R