Add additional lead owner fields with the ability to look up users

Add additional lead owner fields with the ability to look up users

Hi - How can I create additional lead owner fields that show me the pick list to select the lead owner (users)?

I want to set up custom fields (which I know how to do), but I'm having a hard time finding the "Lookup users list" 

I want to create a call back lead owner, 2nd call back lead owner, 3rd call back lead owner etc.