You can easily make your own from wood and a few items from the hardware store.
1. Platform under the grinder with slots for the arm - made from three pieces of particle board. Put a t-nut in the top layer so that you can use a threaded knob to hold the arm in place.
2. Arm - 1x2" hardwood (I used maple). Add blocks on one end to build up the 'shoe'. On mine, I have a shoe on one side for gouges, and on the other side, for the elliptical jig. The critical dimensions for the elliptical jig shoe are that the bottom of the shoe must be 4" below the center of the grinder axis, and the back must be 7" out from the face of the wheel.
3. Elliptical jig - Capt. Eddie has a YouTube video on making this from a plumbing nipple and a length of allthread. He suggested using a plastic nipple - I opted for steel for strength.
4. Platform for grinding scrapers. I made mine from scraps of cabinet plywood, with a sheet of 1/4" aluminum plate on top. Held in place using the threaded knob that also holds the arm in position.
Total cost - less than $10 excluding the wood.