I work in a movie theatre, and at some point I saw something in a
catalog of movie theatre equipment that I can't seem to find now. 
What I'm looking for is a cart used to transport an assembled 35mm
film from one projection booth to another.  

Ordinarily films are transported by using clamps that stop them from
unraveling while you carry the film around, but films are very heavy.

This cart must be about 3'x3'x4", with wheels on one corner.  It can
be tipped on it's side and slid under the film while it's on the
platter, encasing the
film, replacing the need for clamps.  

What I'd like to know is form whom could I buy this, and how much would it cost.