In 2nd Peter, Peter tells is that even though they personally saw Jesus and heard his voice, that they have something more sure than even THAT, the Scriptures.
2 Peter 1:16
¶For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.
17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.
18 And this voice which came from heaven we heard, when we were with him in the holy mount.
19 ¶We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts:
20 Knowing this first, that no prophecy of the scripture is of any private interpretation.
21 For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
Your very sentence denies "the only place His revelation to man can be found is in the Bible"... The Witness of the Apostles IS God's revelation - the Scriptures come to us FROM them.
For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost. 2 Peter 1:21
It is this speaking, as moved by the Spirit, that is God's revelation. You make a presumption you cannot possibly prove - that the Bible encapsulates everything that the Apostles spoke.
Regards