Unfortunately the site search for Wikipedia is rubbish. I always try to check before I create a new article that it hasn't been done before, but googling the site first (and also double-checking in the categories) seems to be the best way to do it. The good news is you could easily merge your list into the pre-existing ones and raise their quality. By keeping the lists focused on one topic, it would also be possible to illustrate every single insignia (so long as there is a photo on Wikipedia or Commons somewhere). Like I said, the list you produced was fundamentally of "featurable" quality (possibly with a little bit of work, but not much) and there are plenty of lists on Wikipedia that are of very low quality yet are inherently featurable if they got a little bit of TLC. You seem to have the skills to do that... so if you want to do some "rescue" missions, there's definitely a job there for you with a rather nice reward at the end. Try not to be too dismayed!