I ran across this message while Googling for the same information. I know that this topic is quite old now but thought it worthwhile mentioning that I ran across the following on Amazon: GeeekPi Micro Connectors Raspberry Pi 40-pin GPIO 1 to 2 Expansion Board 2 x 20-pin Strip Dual Male Header Double Row Straight GPIO Connector Pin Header Compatible with Raspberry Pi(2Pack).
I am currently in the process of making a MagicMirror with a 4GB Raspberry Pi 4B and wish to use 2 units of the 2 mic array for better audio reception to use with MyCroft AI voice assistant. On the surface they seem to fit my needs quite well as well as decently priced. My only concern is whether or not the Raspberry Pi GIOPs can deliver the amount of current to power both units but hopefully will find out for sure with some more research. Thanks to the OP and respondents for providing this information pertaining to the unused GIOP pins. Much appreciated! 