DVDs were taken from the film source - usually 35 mm film - which has a resolution of roughly 2000 lines. 35mm film has been around since its invention in 1892 by Thomas Edison. Since DVD has a resolution of 480 lines, almost no information is lost.
Blu-ray is also taken from the film source, but at a resolution of 1080 lines.
It's not as if the DVD is somehow ported over to a Blu-ray.
Good luck getting your hands on the original 35mm source.