Gallery of Sharepoint Users (not Office365Users)

[Laura3]

Hi there,

I'd like to create a gallery in my app that includes the names of all those who have access to my organisation's sharepoint users (no matter their role). They are more than 1000.

The purpose is for the users of the app to pick a person to whom they assign a project (could be themselves or someone else). I know how to create this using Office365Users but these are not the same as Sharepoint Users. In my organisation for example, there are Office365Users who are former staff that have now left, but they are still in the office users list to keep their emails going etc. 

Any idea how to do this? 

Cheers,