I made a rub from David Klose's Lemon-Pepper recipe where I substituted potassium chloride salt for the real salt. I also reduced the salt substitute by about 1/3 from what David's recipe called for. It made some fine low-sodium ribs. My wife is also diabetic and she uses a product called Spoonable Sugar Twin for baking sugar-free cookies. It is a fluffy white powder. You might substitute that for the sugar in the rubs. But I would think a diabetic could tolerate the small amount of sugar in this recipe as you only use a small part of the rub batch on a slab of ribs.
Mix all ingredients and store in a tightly sealed jar in a cool dark place.