I went to the pelvic floor clinic at GW (near Foggy Bottom) and they were were super helpful! They took my Blue Cross Blue Shield insurance; not sure what other networks they're in.
I went to a PT for DR who gave me very similar exercises to the Helene Byrne's Exercise After Pregnancy book, which I had already been using. I added in hypopressive exercises and, after years + umbilical hernia surgery repair, still have a gap but it's gone from 4+ to 1-2 fingers.
I read many blogs by women and PTs and doctors. A tummy tuck is not the only option, but it will take years to heal. Give it time.