I'd recommend websites like Suitsupply. They have great fabrics and are my favorite place for off the rack suits. Suitsupply
Alternatively, Bonobos has suit separates in a wide variety of different sizes and trims. You go try on the clothes in store then ...
What are you buying this suit for, and what is your approximate budget ? Knowing this will help narrow down the exact brand and fabric style that works best for you!
Rather than taking your chances and trying to find a suit in your size at a local retail or department store, consider ordering a ... StudioSuits