If you don't get a game there (pretty exclusive), then try Hanau-Wilhelmsbad. Sundays are generally very full around Frankfurt. If you don't mind travelling a little further, then you might have better chances, such as at GC Spessart near Bad Soden. If all else fails, you should be able to get a tee-time at GC Bad Vilbel, but it's not the cheapest venue.
I would take you around, too, but unfortunately I am not here on Sunday.
Ulrich