Quaternary ammonium is a popular sanitizing product used in food service. I have easy access to it but I am unsure where you can buy it retail, maybe a US Foods cash & carry store. A manufactuer is Eco Lab,
http://www.ecolab.com/
I run it through my system occasionally, followed by a rinse. To my knowledge it will not react with metal, to address your concern about corrosion, but check the MSDS sheet just to be sure.