You can purchase one here from ChinWorld, but the shipping on it may just eat up your wallet. I would recommend checking the classified ads, as there are often people who sell their old guards. That's how I bought my last Edstrom guard.
I can't answer your question since I have no idea but I thought I would pass this idea along. I have the Lixit bottles and I just use a large flat washer as a metal guard. My chins can't get to the plastic part at all.
All My Chins - that's a great idea - I never thought of that! Maybe a dab of silicone, on the back, would help hold it on - just so you don't have to play catch! [after waiting for a "cure" time!]