Let me share my experience Tom,
When I (Graphisoft AUS) was working on ArchiCAD 16 Australian Template with David Shorter (AUS Strategic technical Manager), We had exactly same problem.
"thermal conductivity" values in INT version of ArchiCAD wasn't correspond to the values in AUS.
I think, the differences are coming from, testing conditions, such as climate, location, method, and "who is testing"
so I started to collect local datas from:
1. Local simulation tools' database
2. Local manufacturers specification (picked couple of major company's data and I used the mean value)
3. Government standard values.
It took me about 2-3months to get typical AUS construction database and still working on this to update this values in the next version.
In terms of density, and heat capacity, to be honest, It was difficult to find relevant indicators, so I decided to reference the values in the standard Archicad database. (but I found most manufactures had this data in their specification).
as a result, We have completed the first version of thermal value localisation into AUS standard template.
We then created new fills with local "k" value and deleted some cover fills with no thermal values.
When I saw Bimcomponent feature in AC16, I was hoping to have similar concept of cloud system where we can post thermal values and share them. Eventually, manufacturers will be in charge of this database and can promote their products at same time.
Hope this information helps,