Hello,
I've forked the code and did a first quick hack to get it to work with python 3.x/calibre 5.x. From my first tests, it works well if you already have the comicvine id, not so well searching the name of the comic.
I did a few changes - allowed setting the request rate (comicvine API will kick you out if you do more than 1 request per second), and the maximum number of volumes to return (1 volume can have several issues) so that it will answer in a "normal" time.
The fork is in my github
here, in case anyone wants to try it.
If you want to just add the ID, put it in the metadata ids field, in the format "comicvine:xxxxxx". The value can be obtained from the comicvine page for the issue you want, it's the six digits at the end of the URL.