Should be 5/16 SAE flare. That is NOT AN or JIC Any good parts store including No Auto Parts Available and O' Really?'s should have them, either flare nuts for tube, or "push lock" hose ends
Actually, ACE hardware might have them, but they might not have 5/16. Most household plumbing (ice machines, etc) use 1/4 or 3/8, no 5/16
These are what is called SAE which is 45* flare angle.