Here’s one of the places selling “kits”
http://therifleshoppe.com/catalog_pages/single_shot_parts/(900).htm
That’s the direct link for rolling block parts. Good luck finding it from the homepage.
http://therifleshoppe.com/default.htm
Here’s the full page of single shot parts.
http://therifleshoppe.com/catalog_pages/single_shot_parts/(single_shot_parts).htm