I would find a glass shop locally that does RVs and/or buses and trucks. An RV windshield is mounted much the same as those on a car or truck. It's the height and size that may be a challenge if you don't have experience from installing them on a regular basis. Definitely not a one man job.
There are companies that specialize in RV windshields. They can ship to your installer, or your installer can order it directly from them. No endorsements, but a quick search found:
www.rvglassparts.com,
www.rvwindshieldreplacements.com,
www.duncansys.com/rv-windshield-replacement and this one which specializes in vintage glass:
rv-glasparts-vintage-motorhome-glass.sqwiz.com. The windshield companies may have an agreement with a local installer or may be able to recommend one.
There is also the possibility of getting a used windshield from a salvage yard. There are plenty of salvage yards that specialize in motor homes, you just have to find one that has your windshield. Most will ship to you. Personally, I would go for a used one only if a new one cannot be found.
Good luck!