Bruce,
If the 1955-1st rear floor mat is the same color (black) as the '54's, then I do not think anyone is selling a replacement mat or even correct material (linoleum) for you to make your own.
Battleship Linoleum used to have the brown in the correct thickness (brown is the color of rear floor mats in earlier Suburbans). If you can find a sheet of black linoleum (in the correct thickness), you would have to machine/route the grooves into the mat (they can provide an article describing how to do it).
Please post a followup here if you contact Battleship Linoleum and if they have the correct thickness of black linoleum (it used to come from Europe but Armstrong? stopped importing it a few years ago).
Tim
