The PiShop apparently does not have the external driver conversion board ( Pololu Socket To External Driver Conversion Board (pishop.us), and I cannot find this animal in the Pololu catalog.

has this thing been discontinued? Does it have another name? Is there somethng else which will work as a pass-thru for RaspberryPi CNCHat?

That is not one of our products. Unfortunately, I do not have any recommendations for an alternative pass-through board like that.