I know that the Hardy Hibiscus (Hibiscus moscheutos) will do well in your zone. Other than that, we'll have to ask one of the experts like
@Horntoad for recommendations, as he even grows quite a few of them from seed.
I know I grew Texas Star Hibiscus aka Scarlet Rose Mallow (Hibiscus coccineus) from seed. Here's a link to the database
Texas Star (Hibiscus coccineus)