Contact these guys. Below is a direct quote from their wer page.
http://www.willrepairservice.com/aboutus.html
We've been in business since 1941...that's 74 years! Yes, we've worked on every typewriter, word processor and many office machines all over the world.
Smith Corona* has sold us all of the their parts, manuals and supplies.
That exclusive relationship is your source
for Smith Corona items,
and is available nowhere else