Maternity Wedding Dresses

I am planning one of my closest friends weddings. She is getting married September 2, the only problem we are running into is her wedding dress. She will be 7-8 months pregnant. Brandy does know exactly what kind of dress she wants, but we are having problems finding it and she isn`t sure when to buy. If anyone could help, both of us would appreciate it (this being the first wedding I have planned, I am not sure what to do!)