I have admired a similar tool as this every time I’d seen an electrician using one, but had not been able to find a retailer or manufacturer.  

Eventually, I found Penthon Tools on Ebay selling a drill attachment that fits some sizes of wire nuts.  I next purchased a Klein cross tip crank-style screwdriver (it has a wider shank than the flat head), cut it off, and attached it to the wire nut spinner using two steel bushings and JB Weld.  

It holds up well and greatly reduces the time and energy of twisting wire nuts on by hand.  Overall cost was about $15 each.