I'm trying to remember the names of the major organizations that put on the shows. You could try the 'trek today' website, it has a popup, but just refresh the screen and it goes away... I'd say Ex Astris Scientia, but that's based in Germany, but if you ever need the tiniest detail, that's the site to check out...
They're sort of tours, so you might check on bigger cities. I live in a city of under a million, so they rarely stop here.
Note - the couple I've been to have been ex-spens-ive! Back in the 90s, it was $30-45 just to get in the door, another $30-50 to attend the question and answer sessions with the actual stars, and the curious and collectibles take a hefty cut as well. Did see Leeta (DS9) walk past me, tho...