Dear Ken:

All of the rosary mysteries are referenced in the Gospels of the Bible except the last three of the Glorious Mysteries.

The Decent of the Holy Spirit references specifically Acts 2, but is promised in the Gospel of John 14.

The Assumption references several passages in the Old Testament from which the Assumption is implied.

The Coronation references Revelation 12.

We could look at this in two ways:

1) To say the Rosary is praying the Gospels, even though there are a couple of exceptions to that, is not a misstatement any more than saying that we always attend Sunday Mass is a misstatement even though, in fact, we miss a Sunday Mass once-in-awhile. It is generally true.

2) To say the Rosary is praying the Gospel is literally true when we remember the meaning of the word "Gospel." The word means "good news." All of the mysteries, whether or not directly referenced in the Gospel books of the Bible, is "good news."

But the real answer is that even though those mysteries that are not referenced directly in the Gospels of the Bible they are implied by the Gospels.

Luke 1 gives us the bases to derive that doctrines of the Assumption and Coronation: Mary is FULL OF GRACE and will carry the Incarnate God in her womb.

If she is full of grace, and is the ark of the New Covenant, then she must be Assumed into Heaven to avoid the decay of her sacred womb and body made sacred by the presence of God who was in her womb. 

Mary, as the Mother of God, the mother of Jesus the King, makes her the Queen Mother (previously imaged in Solomon and Bathsheba) and thus the Coronation is implied.

So, in fact, all of the mysteries of the Rosary are from the Gospel afterall.

God Bless,
Bro. Ignatius Mary