www.vintagefactory.com have stick on foam FMF type
You can also make some out of PVC pipe or use some plastic from a cut up ice cream bucket as its thin and flexible.
You might want to look up Maier universal fork protectors. They make a basic for guard to cover the upper tubes on USD forka that may work for lowers on conventionals. They may be a little big thought diameter wise?
You can also get thick clear or coloured sheet you can stick on.
I would do with getting some PVC pipe of plastic sheet and make your own. I saw one guy make some for a 80's HRC replica CR500 and he used grey PVC pipe and they ended up looking just like the HRC guards pretty much.
Have you tried DC plastics? Look at their unversal RM/TM fork gurds in white or yellow. If they dont have them try Vintage Suzuki.com