Colin, go to a copier shop that does large plans etc and ask them to copy your 1/384 at 300% enlargement. This will result in a 1/128 scale plan.
I use this little program to work out the steps needed.
http://www.modelshipbuilder.com/resources/copierscale.html (http://www.modelshipbuilder.com/resources/copierscale.html)
Mike