Bella's Findings carries them in various sizes/colors, and in 14K and 18K-- Use the search term "hanger" in the search field at the top: https://www.bellafindings.com/
This eBay seller in Texas sells hangers in 14K yellow gold and 14K white gold in 2 sizes. Also in sterling silver and vermeil (yellow and rose gold color).
BWeaves, think about which necklaces you want to use it with, and buy one large enough to fit them all.
I wanted the largest I could find, to fit over multiple strands of tourmaline beads. The Rio and Bella ones were a little smaller and I was not sure they would suit my purpose so I bought a large vermeil one from the eBay seller I mentioned. It measures 19mm long x 9mm wide and fits over a 10mm pearl strand.
As it turns out, it just fits over these beads, so any smaller would not have worked for me. I'm okay with buying vermeil for this purpose. I haven't seen any 14K ones this size.