I live in west St. Louis, and I don't know of any. As you discovered Lake Saint Louis has strict size limits and doesn't allow any ballast. Creve Coeur Lake doesn't allow motorized boats except for special events (the one time I rode there was the best riding ever). Other than that, you've got the rivers Meramac, Mississippi, and Missouri, but I haven't personally ridden on any of them. For lakes you have to go east of St. Louis into Illinois.
I'm newish to both St. Louis and wakeboarding, so I'd love to find out that I'm wrong. Definitely let me know if you find anything.