fatvegan

In template.php or some such...

function site_uc_product_add_to_cart( $variables ) {
  $sku = $variables['form']['node']['#value']->model;
  $stocklevel = uc_stock_level($sku);
  if (is_numeric($stocklevel)) {
    // Stock tracking is active
    if ($stocklevel <= 0) {
      return '<div class="add-to-cart out-of-stock"><button disabled>' . t('Sold') . '</button></div>';
    }
    else {
      return theme_uc_product_add_to_cart($variables);
    }
  }
  else {
    // Stock tracking is not being used for this product, just show the add to cart button as normal
    return theme_uc_product_add_to_cart($variables);
  }
}