So how to find a good jazz dance competition. Most competitions that are out there do have a jazz division which is fairly strong. I think a good way to pick a good jazz dance competition would be to look at their panel of judges and see if they have a jazz background in their professional bios.
Some that I know of that are great is Joe Lanteri's New York City Dance Alliance. Nuvo is a very strong competition, as well as one that I personally judge and MC, which is Spirit of Dance, but that's in the Massachusetts area. If you're in that area, that would be a great one to pick.
And other than that, like I said, just do your research. Go on Google. See the background. If you're really into jazz, you should look at the backgrounds of the judging panel and take it from there. Good luck with your jazz competition hunting.