Hi,
No that's normal. If you don't have access to a product / category / brand, then you don't see it in the products / categories / brands listing, and thus you don't know the URL of the product / category / brand and if you try to access it directly you get a 404 error.
Now I suppose that you created the URL
staging.blazeyuniforms.co.nz/copthorne
with a menu item with the alias "copthorne" linked to this brand. What you actually want to do to redirect the users to the login form when they try to access that menu item is to set the "access" setting of the menu item.
Finally, if you really want to do it with the brand access level for some reason, it's not impossible, but it requires changing the line:
throw new Exception(JText::_('CATEGORY_NOT_FOUND'), 404);
in the files components/com_hikashop/views/product/view.html.php or components/com_hikashop/views/category/view.html.php (depending on the type of your menu item), with something like that:
JFactory::getApplication()->enqueueMessage('you cannot access this page , please login message');
JFactory::getApplication()->redirect(JRoute::_('index.php?option=com_users&view=login'));