Override the taxonomy pages
The template file you want to use is not taxonomy-term.tpl.php; that's used for the taxonomy header at the top of the page. The template file used is node.tpl.php.

If you look at taxonomy_term_page() which is used to build the term page view, you will see the nodes are build separately by calling node_view_multiple(). node_view_multiple() is just a wrapper for node_view(), which uses the standard node.tpl.php file.

Also you should be able to use field_get_items() for taxonomy terms. I'll look for something like $field = field_get_items('taxonomy_term', $term, 'field_name');.

I haven't tried but it should work. 

You should really never use 'und', but the constant LANGUAGE_NONE.