Reminder Screen

I am trying to figure out the reminders and hoping the solution is simple.

Since we can only assign reminders for people in our control group many of us are unable to assign tasks to other departments, which is actually the whole point of having this option - so the Box Office and Development and Events can assign follow-ups to each other. Any work arounds with this? I have no one in my assign reminder drop down and others don't have anyone but within their team. Making us a manager user isn't feasible or possible. 

Appreciate any help!

Jen