You might try Lange's Deli in Bronxville as they do cater, and have a good reputation for food. It's on Pondfield Road in the village, corner of Park. Topps Bakery is also nearby if you need pastries for your event.
Lange's Deli of Bronxville
Another place you might try is the Pelham Gourmet Deli, which is off the Boston Post Road, right at the Hutch, on West Street. If you are familiar with BJ's and Fairway, Pelham Gourmet is across the Boston Post Road, and West is the small side street that is just before the discount cigarette store that is on the right, immediately at the Hutch.
Panera also caters, though it depends upon location as to how good a selection that you receive as some Panera locations have better trained kitchen staff, I find. The location on Central Avenue is pretty good, so it would give you another place to compare.