Apparently a pattern/brush no one who has it wants to share. I've also sought this out on other wargame design forums without success. I can offer you a scan of this which I purchased back in the 1970s for the same purpose, albeit for use on that ancient material called "paper".

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Link to 10 MB 600 dip TIF scan here:
https://drive.google.com/open?id=1cm...s2si7WhJ2qgUWL

Although I'd prefer a clean digitally created version, I've managed to manipulate this to meet my needs. Good luck.