You should be able to find a replacement/upgrade. The thing I found frustrating is how brake line size and thread type are shown.
Here is an example of what might work, says for 1/4 line. You want "female" when the threaded end going into the fitting. The end of the brake line is termed "inverted flare" so you want a fitting having the "female inverted flare."
https://www.amazon.com/Stop-Shop-invert ... 400&sr=8-8This may work for the smaller 1/4" brake lines and then get an adapter brake fitting/reducer that will accept the larger line coming off the master cylinder (female inverted flare) and then screw into the 3-way ("male inverted flare) on the other end of the adapter.
Some of the local autoparts stores like Advance Auto have a selection of adapters, but don't expect them to be of much help as you want to know the correct size because they won't.
Another place to look or contact is Speedway Motors. They specialize in hot rods ad have things like the banjo bolts, copper washers (if needed), adapters, lines, etc.. If you don't see it online, contact them and they can most likely help.
Earl's is also another supplier of brake parts and may be able to help or have what you need.
Much of working on the older Internationals seems to require fabrication or modification to make things work - it's not like a Chevy or Ford truck where many of the parts are available or reproduced.