add_filter( 'asp_post_custom_field_before_tokenize', 'asp_tokenize_sku_variation', 10, 3 );
function asp_tokenize_sku_variation($values, $post, $field) {
if ( $post->post_type == 'product' && $field == '_sku' ) {
'post_type' => 'product_variation',
'post_status' => array( 'private', 'publish' ),
'post_parent' => $post->ID // get parent post-ID
$variations = get_posts( $args );
foreach ( $variations as $variation ) {
$sku = get_post_meta($variation, '_sku', true);
if ( count($skus) > 0 ) {
$values = array_merge($values, $skus);