Just in case google has led anybody here looking for help:
The file you are looking for is 1042.mst in your installation source folder next to the existing *.mst files. (i.e. C:\Program Files (x86)\Adobe\Acrobat 10.0\Setup Files\{*******-****-****-****-**************}\
You can find 1042.mst using google:
www.2shared.com/file/qx8UbgcG/1042.html
https://www.dropbox.com/s/estb3wcgqradv8h/1042.mst
Place the 1042.mst file in the installation folder and run the setup. Retro-installing on existing installations can be done by running setup, then choosing "modify".
Under "Create Adobe PDF", select/expand "Asian Language Support" and select the Korean package for installation.