In a pinch, try Tractor Supply or Rural King. Not the least expensive place to find supplies, but I've always seen jars and a few supplies at all the TSCs I've been to. Usually I wait until canning season is over and stock up on the mark downs, and put them up for the following season.
I can eat night shades but my kiddo has major allergies and neither of us can have gluten, so baking or canning is often very challenging. I have tried baking with coconut flours, almond meals, an even ground flaxseed.
Canning has gotten a little easier since kiddo outgrew the tomato allergy, but drying foods in a dehydrator worked well for us since I didn't need to add anything to the foods to preserve them.