Resort get_categories

There is already a function in WordPress doing that: wp_terms_checklist(). It is used in the metabox for hierarchical taxonomies in the post editor. Maybe you can reuse that?

The following is untested, see it just as a guide please, not as a complete solution:

// File where "wp_terms_checklist()" is declared
require_once ABSPATH . 'wp-admin/includes/template.php';

// Output will be printed immediately
wp_terms_checklist(
    0, // post ID
    array (
        'descendants_and_self' => 0,
        'selected_cats'        => FALSE,
        'popular_cats'         => FALSE,
        'walker'               => NULL,
        'taxonomy'             => 'wpsc-variation',
        'checked_ontop'        => FALSE
    )
);