You should be able to add a piece of metal or some rigid plastic to the underside of the slotted guide and have a 3/16" (4mm) bolt & lock nut hold it together. That should then do the same thing as my mod, allowing the added piece on the underside to be held in place and slide on the slotted guide. You shouldn't need a replacement.
EDIT: I should add that it was not my idea/mod. It was the brainwave of sefj1100 (Scott) on the Australian forum in 2011.