It should be a standard gear cable, the round bit in your picture is a bushing that you feed the gear cable end into before attaching to your post and threading through your frame?
This is a picture of the bushing;
You should be able to remove the bushing from yours and re-use it.
I bought the Jagwire dropper post cable. It is a little smaller diameter, slick, and works great with my FOX dropper. That piece is an add on. I do not remember if my kit from Jagwire came with a new one or if I reused my old one, but the kit worked slick.