There is a coax plug and socket pair in the forum that I made several years ago. It was an experiment to see if the combination could be made to auto connect (which it can.) It looks to be here:
When in need of a part the first thing I do is run a google search of the form “fritzing part 2.1mm male jack” (or whatever I am looking for) to see if there is a part already around somewhere. Only then do I start thinking about making one. That is how I found the above referenced forum posting.
Peter