That's wonderful, and this is what you can do, if you move quickly. In the US, the president ( that's right, him) will sign a letter congratulating your parents for 50 married years or more. Not sure if two weeks or so is enough time, but worth it. Even though you may not enjoy this particular man in charge, your parents might appreciate the formal recognition.
50th is traditionally gold. Any brothers and sisters? What you can do is pool your resources and buy them these: Find out what the traditional birthstone for the month they were married is. Get Mom a small gold locket with the stone inset- it can be real tiny. Get Dad a gold tie tack with the same stone embedded, once again the stone can be very small, as it's the symbolism that counts. These are keepsakes, not necessary to wear.
We both wish them all the best and much more in the way of continued years together!
-D & B