Help with Item duplication mod

Im making a mod that adds an Item Duplication table, and i want to make it always duplicate to the full stack of a specific item, except some items have different stack amount, Is there any way to make a procedure check what is a maximum of a specific item in one slot?

Below is an image of a procedure of a gui that duplicates items, it always makes 64 items, which usually is a stack but for something with a small stack it makes a mess in player's inventory: