[folivier]

Looks like a 1/4"npt elbow x 1/4"? tubing fitting. Napa should have that fitting, also Grainger, McMaster, and others.
Is it leaking where the plastic tubing fits into the fitting? If it's a push on fitting and you have enough slack in the tubing you could pull out the tubing by pushing in on the ring, cut off about 1/2" of the tubing and push it back in. Lots of times the tubing will develop a leak especially if there is any sideways tension on the tubing.
If you replace the fitting try to find a compression type fitting rather than a push on type.