Official XBRL taxonomies are usually downloaded from official taxonomy sites, such as: www.xbrl.org
Popular taxonomies are available at:
http://www.xbrl.us—US taxonomies, such as US GAAP 2009
http://www.iasb.org/XBRL/IFRS+Taxonomy/IFRS+Taxonomy.htm—Current IFRS taxonomy, such as IFRS for 2010