Addons are a very recent addition to the Badgegen updates. As of today, I have not encountered any tool that would help you automate what addons you still need for the next leap day. One thing to keep in mind, diamond is not always required to see an addon. With a few exceptions as described in the link you provided, gemstone (ruby) is the first level where addons will appear. I have several leap day addons I can't see, yet, because I need to boost my numbers from medals to the ruby gemstone.
Since the next leap day is approximately 4 years away, I suspect that PGC could very well implement tools that would help to automate the process in determining what addons you still need. Perhaps you might change your category to Feature requests to get it on the To Do list.