Like Duncan, my Peter "Bushy" Robinson Slotting Tool for a Series 7 Myford now sits on a packing block to suit my 6" centre height lathe.
As already said, if you can't find a secondhand one that can be adapted, you could make one. If you choose to go down this route, my preference would be to use sealed ball races rather than bronze shoes to steady the workpiece.
By making your own, you may be able to produce an item that meets your needs more exactly than a proprietary item.
There have several articles in the Model Engineering press on making a steady for a particular lathe, or for some job that is too big for the "normal" device.
Howard