We have a limited number of Mossberg 500/590 14" barrel conversion kits and they are $379.95 for the complete kit. I'm pretty sure this is a one time but for us.
http://www.theammosource.com/index.php?main_page=product_info&cPath=14_192&products_id=6357
http://www.theammosource.com/index.php?main_page=product_info&cPath=14_192&products_id=6357