The solenoid spring for a Rittenhouse 2-tube door chime is to weak to dong. It will ding when energized but won't spring back hard enough to dong. I would like to know where I can get new one?

What you have described is a typical symptom of weak batteries if the chime is battery-powered. It may be a good idea just to try replacing the batteries by a brand new set. <><><> Try ElectraChime at www.ElectraChime.com

ElectraChime has a beautiful selection of modern and period correct Long Chime door bells.