All verses quoted in NASB
Based on Isaiah 61:10
I will rejoice greatly in the LORD, my soul will exult in my God; for He has clothed me with garments of salvation, He has wrapped me with a robe of righteousness, as a bridgegroom decks himself with a garland, and as a bride adorns herself with her jewels.
and Zechariah 3:4
He spoke and said to those who were standing before him, saying "Remove the filthy garments from him." Again he said to him, "See, I have taken your iniquity away from you and will clothe you with festal robes."
it appears that God is the one who clothes the saints with the necessary wedding garments. I believe the best way to reconcile the concept of the bride making herself ready in Revelation 19:7-8
Let us rejoice and be glad and give the glory to Him, for the marriage of the Lamb has come and His bride has made herself ready. It was given her to clothe herself in fine linen, bright and clean; for the fine linen is the righteous acts of the saints
with the old testament verses showing the Lord doing the clothing is through John 6:28-29.
Therefore they said to Him, "What shall we do, so that we may work the works of God?" Jesus answered and said to them, "This is the work of God, that you believe in Him whom He has sent.
Therefore I believe your last suggestion is the right conclusion, that the righteous acts of the saints is their faith in Christ.
In addition, the context of Matthew 22, the parable of the marriage feast, is similar to parables in Matthew 13 of the Tares among Wheat (verses 24-30 and 36-43), the Mustard Seed (verses 31-32), the Leaven (verses 33-35) and the Dragnet (verses 47-52).
Each begins with "The Kingdom of heaven may be compared to..." or "The Kingdom of heaven is like..." The overall theme of these parables is that the enemy has sown sons of the evil one in the kingdom of God, which the Lord has let remain so that the sons of the kingdom are not uprooted. (Matthew 13:29 and 13:38-39)
Although a son of the evil one may not be distinguishable from a son of the kingdom by outward appearances, believers are sealed with the Holy Spirit, as seen in Ephesians 1:13:
In Him, you also, after listening to the message of truth, the gospel of your salvation - having also believed, you were sealed in Him with the Holy Spirit of promise.
We know from 1 Peter 4:14 that the Holy Spirit is the Spirit of glory and of God. Now, hold onto that just for a minute, while you bear with me for one more thought. Philippians 2:6-8 says about Christ Jesus:
who, although He existed in the form of God, did not regard equality with God a thing to be grasped, but emptied Himself, taking the form of a bond-servant, and being made in the likeness of men. Being found in appearance as a man...
Per Strong's, the word "emptied" if from "kenoo" which means "to make empty, to make void." However, during the transfiguration, Jesus was seen as glorified. Matthew 17:2 says:
And He was transfigured before them; and His face shone like the sun, and His garments became as white as light.
and Mark 9:2-3 says:
And He was transfigured before them; and His garments became radiant and exceedingly white, as no launderer on earth can whiten them.
In light of all this, since believers are sealed with the Holy Spirit, the Spirit of Glory, I believe the Holy Spirit may consitute the wedding garments of the saints.
This would be futher supported by the Parable of Ten Virgins in Matthew 25, which closely resembles the Parable of the Wedding Feast. All of the virgins took their lamps, but the foolish had no oil to light their lamps. (verses 3-4 and 9) Verse 10 says:
And while they were going away to make the purchase, the bridegroom came, and those who were ready went in with him to the wedding feast; and the door was shut.