reply to u/Ill_Tear8308

Not so much that they're proprietary, but the Zephyr, Skyriter, and later Corsairs used the 1 5/8" diameter spools, which fit about 12 yards of ribbon versus the more common universal 2" spools which will hold 16 yards of ribbon.

1/2" wide ribbon should work on this. Sellers include: https://site.xavier.edu/polt/typewriters/tw-faq.html#q1

If you wind it onto pre-existing spools keep in mind that Smith-Coronas typically used eyelets in the ribbon to effect the auto-ribbon reverse, though you could certainly do it manually if you needed to.

There aren't a lot of examples of Empire-Coronas in the typewriter database, so be sure to include your example with photos:

https://typewriterdatabase.com/empire.24.typewriter-serial-number-database

https://typewriterdatabase.com/Empire.-Corona+Skyriter.24.bmys

Empire Sky-Riter Typewriter Review by Smith Corona: The End of Empire by [[Lazy Dog Typewriters]]

Around 1960 Smith-Corona bought out British Typewriters Ltd. (aka Empire) in West Bromwich, England and used the plant to make a version of the Smith-Corona Skyriter which they sold under the Empire name.