Perhaps nismo makes some? If not, I’m sure they’d whip up a design for you, even though it might not fit into your budget. 😛
You could always go to home depot and get some fiberglass kits and make your own, if you like weekend projects. You’ll get the benefit of having a 100% original wing, too.
Consider looking for wings made for other minivans, then fitting them to your quest. Again, it may be out of your budget, but there are a lot of Japanese aftermarket parts makers that make nice spoilers for JDM vans that you could modify. I would Suggest looking for wings intended for the Nissan Elgrand, Toyota Estima, or Toyota Alphard/Vellfire.
(Sorry for this huge topic bump…)