You can pick one up at Home Depot today. Go to the plumbing section and find the 1/2" tubing to 1/2" FPT John Guest fitting. Take a 1/2" drill or dremel tool and carefully drill or cut the tubing stop (the lip that prevents you from inserting the tubing in too far) out of the fitting. Be careful not to cut the O ring that seals the tubing in place.
There you have it! I have one of these in service for 2+ years, no leaks!