What type of "blueprints" are you looking for? If you mean parts and assembly drawings for various aircraft, these have become quite commonly available to the enthusiast and historian or restorer. I've had the NAA P-51microfilm for years. Lately I've added several CD, DVD's etc. Just found compete P-40 drawings I'd forgotten I had. Also haveF4-U drawings and P-26 and P-12 microfilms, so it is available.
BTW, true "blueprints" went out of style during WWII, especially in aviation industry. The new copy process was "ozeloid", which had a blue (purple actually) line on a white photo sensitive paper. This process has been recently replaced with digital reproduction.