I seen them on e-bayI don't see indevidual bolt on, just weld on shanks in our catologs. I can get serrated bolt on cutting edges, if thats of interest.
http://virnigmfg.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=52&category_id=11&option=com_virtuemart&Itemid=78#
Ken