Well, I cannot offer an authentic capture of an IT8 from the 19xxs – but perhaps we could work something out nevertheless? @Morgan_Hardwood
My idea is that you look through your slides to see if you have captured any well-known object that was made/printed with close colour tolerances.
A few examples of suitable objects:
A yellow Kodak box/logo/envelope (search for KODAK Publication Z7-1 to see the specifications).
Heinz tomato ketchup (search for Heinz visual identity guidelines)
Car brands, McDonald’s, Burger King, gas station logos, food store chain logos, sport teams…
However - beware that the company’s guidelines may have been tweaked a little since you caught their logo on a slide. Coca-Cola, for instance, is known to have changed during the decades.
Have fun!
Claes in Lund, Sweden