Air conditioning hose will hold with hose clamps which is higher pressure. The return line is open to the tank after the pressure regulator. The manufacturer uses a good quality crimp fitting. But a good quality high pressure hose and hose clamp should hold. You can buy high pressure hose from ebay suppliers.
I would go to U-pull it and find a chev. malibu and snip a piece of hose at the metal lines and go to Home Depot or Lowes and buy two copper crimp splicers.
Sometimes a scrap yard is a good source for parts that fit. I have used hose clamps on air hose carrying over 100psi and they held. These fittings might work.