On a whim, I purchased some 1.5mm clear beading cord and notions on sale at Michael's.
These are photos of the hair ties that I came up with.
If you want to purchase the real deal, professionally done hair ties for locs and sisterlocks, you must check out Tomoka's Twists. I like Tomoka's Twists because they are made with coated wire. You can control the tension on your hair better than with hair ties made with elastic cord.
The beading cord that I used is smooth and doesn't catch hair to damage it, but Tomoka's wire hair ties can be positioned any way you like.
Brunsli's Hair Ties are gorgeous too, although, there were no hair ties for sale in Brunsli's Ebay store when I last checked.
Mwedzi has a good "how to" video on Youtube, if you would like to make your own hair ties. Check it out.