As Zachary said, needles can be welded back together and will work fine. I've had a couple welded over the years. To be exact, I think that they were actually brazed.
If you can't find any new or used needles, you might consult a machine shop to see if they can fix your broken ones. There's little or no actual stress on the needles. They never contact any hay. They don't penetrate anything. They just deliver the twine to the knotters.
Tom in TN