I assume you mean the metal support the plastic flare sits on?
They are very easy to make yourself if you can't locate any. Get a strip of metal of the right thickness and wide enough to support the flare, attach it in position with a couple of rivets either end, get a permanent marker and reach inside the guard and draw the contour of the guard, sit the plastic flair in position and hold with a couple of small clamps, then draw the shape of the flare, then remove the strip of metal and cut to shape with some tin snips. I have made a few sets that way and never had any problems. Just a way around it if you can't get any.