I have sets of 1/8" - 1 1/8" in 1/32" and 1/64" increments from CDCOtools.com. I haven't had problems with any of their collets. However, I don't see individuals for sale from their web site. I added 1/16", 5/64", 3/32" and 7/64" collets from CME tools in Madison Heights, MI for around the same cost as from Shars. I've had good luck with stuff from Shars as Dave mentioned above.
Amazon has quite a selection. Including Hardinge
I have the CDCO and they have done good for 6 years. Only thing is the threads are not all the same size. After stripping out a couple of
drawbars I marked the undersized collets and use them in a separate drawbar that has smaller threads to match them.
I also made replaceable hardened ends for my drawbars.