Taxonomy Tag Conditionals

Question

I'm using jigoshop as main ecommerce plugin.

Jigoshop use Taxonomies call, product_cat and product_tag.

In my theme I use a default (h5bp) 404.php, so every time a tag doesn't exist I get the default 404.

But I need to have a special template that give a THIS TAG DO NOT EXIST

how can I do this?

I'm using pointless:

@@@
<?php

if (is_tax()){
    jigoshop_get_template( 'product_taxonomy-no.php' );
}else{
 jigoshop_get_template( 'product_taxonomy-no.php' );
}
?>
@@@

thanks