I am trying to search for information on 3 speed manual transmissions. But everytime I try the search function deletes the "3" or "three" because it is too common or short. What gives? Any hints here?

Try searching for "Saginaw" and "transmission". Three speeds were typically Saginaws.

Yep, Saginaw would be good, but just try "manual transmission" and sort out those you want.