I just did extensive searching. It appears that SW no longer sells the copper tubing kit, only nylon. On ebay however you can find the kit cheap. no offerings of fittings only but the price is right. It appears that the ends are soldered on.
https://www.ebay.com/itm/Stewart-War...-/182736982845
https://www.ebay.com/itm/Mechanical-...0AAOSwivdcuOMZ
https://picclick.com/Stewart-Warner-...736982845.html
Glenn