I can't really tell from the pic what the fitting does. Is it just a compression fitting to connect the tubing? If so bring it with you to Home Depot or Lowe's and they may have something that can work for you.
Features: White acetal construction EPDM O-ring FDA approved material NSF Certified 51 & 61 Suitable for water & food applications Available in bags of 10 or Box Quantity of 500