Maybe not Equisetum giganteum, but how about Equisetum myriochaetum, native to some South American countries, or some 5 other taxa? See site linked below.

And while this site does not seem to be searchable, perhaps contact the Liege Botanical Garden to see if they have any:
http://www.espacesbota.ulg.ac.be/en/serres_historiques_histoire.html

Or this may be helpful: http://www.bgci.org/plant_search.php

Here is a link that might be useful: National Botanic Garden of Belgium