After moving to a new home, I found extra sliding shelves, but no brackets to mount them. I took apart the existing shelves, copied the bracket design and added my own structure for stability and support in place of the original metal pieces.

I chose to print the pieces in ASA with in-fill at 60% to give increased support to the brackets.

Each shelf requires 4 brackets: Left-Front, Right-Front, Left-Back and Right-Back.  I've included here one Front and one Back piece, both for the Left side.  Just mirror the included files along the X axis to create pieces for the Right side.  See the photos for reference.

The Photos show 3 of the original pieces (in grey), and the 4 printed pieces (in black).  From the originals, it should be clear that the left and right sides are mirrors of the same pieces.

These pieces are large and complex, and should be printed with high in-fill for best ability to hold the weight of the shelves and their contents. It is advised to first print low-quality pieces (using PLA and low in-fill) to ensure they fit your shelves before using a lot of filament and time on the final print.