Does anyone know what I can send my deployed husband so he can heat up canned foods?

I'd say just buy a hot-plate. I've seen the heater coils you're speaking of but they would just get caked with soup and be nasty. The only issue would be what his detachment's electrical requirements are (the DoD is usually anti-hotplate because of the fire hazard). You can get around this with a mini crock pot though.