I have been unable to find a site where you can download a Smith Corona typewriter manual. However, you can try going to Will Repair Service
. They carry manuals of every Smith Corona typewriter ever made, and you should be able to find a manual for your particular typewriter there. I find them to be a very helpful and trustworthy typewriter shop.
YES, SMITH CORONA DOES STILL EXIST!
Best of luck to you! :-)