Try here

www.antiquecrawlerparts.com

you could also try a rare spares stockist they have a range of windscreen rubbers

I replaced many of the glass panes on my No. 12 early last year. Here are my suggestion:

• Don't bother trying to use the old moldings; they are hard and not flexible (I couldn't get them to work for me)
• The molding that I used for doors, sides, and lower front windows was from TRIMLOK.COM, part number LK1179.
  • The molding worked very well but I had to have the replacement windows sized 1/8" shorter and narrower to accommodate the molding size difference.
• The molding that I used for the outside of the front and rear window frames was SWISCO.COM, part number 40-207 (Larson Storm Door Sweep).
• I used 1/4" clear laminated glass.
  • I cut the glass myself but if I have to do it over again I would hire a professional to cut the glass.

Hope that this is helpful... It would have been for me.
 

Your grader looks real nice.  

I went with the CAT replacement per the post above. It is actually a bit cheaper than many of the aftermarket sources and fits beautifully. It is made differently than the original, but when installed, you can't tell the difference.

  I thought I'd post a picture of the grader with its new windows. It was so hot I only installed the broken panes with used unbroken glass panels and new seals. I'll replace the other two when its cooler. I also had a stroke of luck. The external oil manifold was leaking somewhere and the oil was pooling on on the base of the oil filter housing. I assumed the worst, but once I got it all cleaned off so I could see from where the fresh oil was coming, one of the cast fittings soldered onto the oil tube was barely finger tight. Once I tightened it up consistent with the other 6, it stopped. So a banner day.

some times sheer arse beats class and you can get a win fairly easily.