I have contacted two companies that do magnetic striping for super 8 and 16mm footage. They can do a single mono strip or a double stereo strip. Very nice people to deal with. I will be adding them to our "Film And Film Related Sellers" link soon, but for now here are the links to their websites:
FFR Film Filmtechnik http://www.ffr-film.deFritz Jäger Magnettonfilmbespurung http://www.filmbespurung.de/FFR Film Filmtechnik also has many accessories including sync devices.
You can use "Google Translator" if you need to change these sites to your language.