I seem to have entered the most items under Exonumia. In fact what I think you should have is a checkbox to indicate that the item is exonumia and still allow it to be classified under its country. NCLT might be another attribute to add at the same time.
With these two options you could enter a medal under France, check it as exonumia and someone looking for French medals would be able to find them easier. Since they would be separate database attributes you could add them to the search page to allow further filtering.