I have only once seen one for sale here on the EE and one for sale on gunbroker over about a two year period. Earls will be your only option and you will pay dearly! Good luck -
Why a factory barrel? Why is Jarvis out?. They had them in 07 which was the last time I looked Nope they still have them.
http://www.jarvis-custom.com/Products/tabid/53/ctl/ProductDetail/productId/21/mid/388/Default.aspx
If you need a threaded barrel why look for a unicorn? Jarvis is good kit.
There's one in the EE right now.