if you are going to chain reswtaurants, you can,t expect alot of special diet consideration.
i would suggest looking at different types of restaurants that tend to cater to people that have dietary modifications.
natural food & vegetarian restaurants are the way you may need to go. these typel of restaurant, especially in larger cities, are not"hippie" joints, and can be very creative and tasty without using alot of sodium.
if you are in a serious medical diet modification need, you may just have to start to change the way you eat