Dynamic href link to Contact Page

If the contact page is identified solely by the associated template, you can query for a page with the template name in meta key _wp_page_template:

$args = array(
    'post_type' => 'page',
    'posts_per_page' => 1,
    'meta_query' => array(
        array(
            'key' => '_wp_page_template',
            'value' => 'contact_template.php'
        )
    )
);
$contact_page = new WP_Query( $args );

if( ! empty( $contact_page->posts ) )
    echo get_permalink( $contact_page->post->ID );