I don't think they've had one for a couple seasons now. The only ones I know of for certain are Toronto and Seattle. Toronto have worn all 3 of their kits in competitive matches this year, and Seattle made a big announcement about theirs just a couple weeks ago.
As for everyone else, info is tough to come by. If you go to the MLS online shop, about half the teams only have replica jerseys available, with no on-field authentics. It's aggravating. For this project, it took me about twice as long sifting though photos to find all the collar, sleeve, and piping details as it did to actually draw them. And if you've surfed MLS's new website looking for photos, you know how big of a pain in the arse that can be -- I'm an American so I love MLS, but their website layout is all kinds of horrible.
Anyway, if there are other teams with third kits, I'd be happy to make them, provided sufficient photo evidence.
Amazing minis, but where is Colorado Third, they didn't used it in this season?