You can make your own spool cap . This will work if you are putting the spool on horizontally. It just needs to be a tiny bit bigger than the end of the spool. You can use any rigid material. I have used cardboard, template plastic , the pastic from a micro meal etc. The cap allows the thread to feed slightly upward , instead of across the end of the spool where it gets caught in that little notch. Many of the spools a few years back had the notches on both ends.
If you are feeding the thread so that the spool stands on its end ... tape the cut in the spool with a small piece of tape.