You are quite right there, C:\Program Files\darktable\share\lensfun\version_1 holds the xml files.
Among them is mil-panasonic.xml where I guess the relevant code is. It starts with lensdatabase version = “1”, the file is 1 943 lines if that means anything to you.
Does this file exist on a Linux installation? In that case maybe it is possible just to copy that single file?