I think HVAC PEX tubing is probably similar to the plastic air brake tubing, you can get it at the big box home stores, I don't know the price difference but worth a look.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy