I really love the way end caps finish off a piece of coiled wire jewelry. I do wish that I could direct you to a source so that you can buy them. At this point, however, the only way that you can get end caps is to make them yourself. You will either have to cast them or take a piece of tubing and solder an end on it.
BUT -- there is a little bit of good news for capping the ends that is very simple and it gives your piece a finished look. This project will show you how to do it.
STEP 1—Take a ¼” tube and cut a piece the length that you want. Unless you are very good at cutting tubing and making a square cut, I suggest getting a tubing jig to hold the tube as you cut. (Figure EC-1)