To retrieve all the terms attached to your taxonomy “brochure_categories”, you can use get_terms()
function. More info here.
Once you’ve got your terms, you can traverse them and query your custom posts with:
$query = new WP_Query( array(
'post_type' => 'brochures',
'brochure_categories' => $current_category,
'posts_per_page' => -1,
'order' => 'ASC',
'orderby' => 'title',
) );
You can now display them, by category, as it suits you.
Is it ok for you ?