We cannot find piano boards online, check with your local mover.
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Types of Piano Boards

Piano boards are a specialty item for the professional mover.  Most piano boards consist of a long padded board with a small stop at one end.  There are handles attached to this board and spaces to attach logistics straps.  

The piano is attached to this board (a grand or baby grand piano would have its top and legs removed first).  Being attached to a piano board protects the piano and makes it easier to grasp and move.  Once on a piano board, the piano can be slid along stairs or placed on a four wheel dolly.