Short answer is bring your own if possible. However, I have borrowed one from Hendrickson before. My student had to ask the monitor, who had to find a director, who had to find a marimba, who had to bring to down to the room, to find out that it wouldn't fit in the door, who found another one, get it into the room, etc.
My student really didn't have any time to play the instrument before his performance. Still did well (2), but our own instrument would have been helpful.
That all being said doesn't mean the same applies this year.