A Teacher's Trunk on Wheels

Of course, some teachers use the trunk of their car as their office and go to it between classes to restock.  I've done that too, but since August 2010 (I looked it up in my Just the Facts timeline) I've had a really wonderful square trunk that I got from Office Depot.  Everything fit.  It was easy ot find things--like carrying around a file cabinet.  But I noticed some resistance a couple of days ago and thought something had gotten on the wheels to make them move less easily.  Instead it turns out that I lost a wheel. What could I do?  I got it to the car on its one remaining wheel, and then before I put the trunk in the trunk, I took its picture.  I went online and couldn't find another like it--not under file-on-wheels or rolling file or cart-on-wheels.  (I guess a cart always has wheels.)