As a retired product designer, I suggest... if you could ask an engineer friend or friend of a friend to create a large format graph with their Computer Aided Design (CAD) software and print several sheets for you that would be a sure thing.

I believe that if you photocopy anything at the local copy store the copy will automatically be a fraction smaller. Rumor was that was law to inhibit counter fit money printers?

https://www.alvinco.com/Shop/Products.aspx?IID=13876

ALVIN Company is a well known engineering supplier who should be accurate, contact them and ask them about the accuracy of there graph paper.