Amazon has a bunch of them on Prime. I used the search term "ribbon wire 20p".
Pc Accessories - Connectors Pro 100 Feet Spool 1.27mm 20P IDC Flat Ribbon Cable for 2.54 mm Connectors, 20 Wires, 20C
https://www.amazon.com/dp/B00RX55SZW..._-N2FybRD9E5KE