Hello @ShawnHarahush
Thank you for contacting the Canvas Community. We're sorry to hear you've been experiencing issues with teachers sharing item banks with one another. By default, they should be able to do this without adding each other to their courses, exporting/importing, etc. When they open the item bank option, they can view theirs in the course -but the course has a dropdown option and one of them is institution. If the school gets versions of these item banks and they should, then any teacher should be able to simply search institution for the title of the course.
Here is the Canvas guide:
https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-manage-item-banks-in-New-Quizzes/ta-p/1...
Hopefully this helps.