When we first went to zipcord style wiring, we were able to get some (limited selection) locally from RadioShack (back when it was a thing), since they sold it as "speaker wire". More recently we just ordered in bulk from McMaster:
https://www.mcmaster.com/#standard-e...-wire/=15adlbs
(Click the link, then select "2" under the "number of wires" option and "12V DC" under the "Voltage" option)
It's a bit harder to separate than the stuff you can get from AndyMark (or the older stuff we got from RadioShack) but works great and definitely helps clean up cable runs and keep sets of wires together.