Just quickly searching, I found this for you:
The assertion that dead saints cannot hear our invocations rests on Ps. 115 , 17: “The dead do not praise the Lord…” It should be noted that this Psalm was written at a time when Jewish understanding of the after-life was not yet fully developed. By the second century B.C. the Jews would have a better understanding of both the after-life and the intercessory role of the dead:
“What he saw was this: Onias, who had been high priest, a noble and good man, of modest bearing and gentle manner, one who spoke fittingly and had been trained from childhood in all that belongs to excellence, was praying with outstretched hands for the whole body of the Jews. Then in the same fashion another appeared, distinguished by his gray hair and dignity, and of marvelous majesty and authority. And Onias spoke, saying, This is a man who loves the family of Israel and prays much for the people and the holy city - Jeremiah, the prophet of God. Jeremiah stretched out his right hand and gave to Judas a golden sword, and as he gave it he addressed him thus: Take this holy sword, a gift from God, with which you will strike down your adversaries” (2 Macc. 15, 12-16)*; *
At the Transfiguration on Mount Tabor, Moses and Elijah appeared talking with Christ (St. Matt. 17, 3). This would have been impossible if they had been “dead” according to the Protestant understanding of Psalm 115. In relating to the Pharisees the parable of the Lost Sheep, Christ stated that “there is joy in the presence of the angels of God over one sinner who repents” (St. Luke 15, 10). Further, in His discourse to the Sadducees, Christ declared that the just dead are “equal to angels” (St. Luke 20, 36) for God “is God not of the dead, but of the living; for to him all of them are alive” (St. Luke 20, 38). Hence, it follows that both angels and humans in heaven are aware of what is transpiring on earth. Finally, as if to emphasize the power of the dead to intercede for loved ones on earth, Christ proceeded to relate to the Pharisees the story of Lazarus and Dives:
“The poor man died and was carried away by the angels to be with Abraham. The rich man also died and was buried. In Hades, where he was being tormented, he looked up and saw Abraham far away with Lazarus by his side. He called out, Father Abraham, have mercy on me, and send Lazarus to dip the tip of his finger in water and cool my tongue; for I am in agony in these flames. But Abraham said, Child, remember that during your lifetime you received your good things, and Lazarus in like manner evil things; but now he is comforted here, and you are in agony. Besides all this, between you and us a great chasm has been fixed, so that those who might want to pass from here to you cannot do so, and no one can cross from there to us. He said, Then, father, I beg you to send him to my father’s house - for I have five brothers - that he may warn them, so that they will not also come into this place of torment” (St. Luke 16, 22-28);
“Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight and the sin that clings so closely, and let us run with perseverance the race that is set before us” (Heb. 12, 1)*;
“But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, and to the assembly of the firstborn who are enrolled in heaven, and to God the judge of all, and to the spirits of the righteous made perfect” (Heb. 12, 22-23).
*In this last passage St. Paul explains to the faithful that although they are still on earth, they are in communion with the heavenly Jerusalem and with the dead Saints, those righteous made perfect.The faithful on earth are not in communion with the bodies of the Saints buried in peace, but with their souls. Death does not inhibit this communion.
I hope that helps.