It's well-known that the Mahabharata and the Srimad Bhagavatam have apparent discrepancies in regard to Vyasa's son Shuka. In particular, this chapter of the Shanti Parva of the Mahabharata describes Shuka attaining Moksha before the Mahabharata war, and yet Shuka is the one who narrated the Bhagavatam to Arjuna's grandson Parikshit, long after the war. But this excerpt from the Tirumala Sthala Purana, the temple scripture of the world-renowned Tirumala Venkateshwara temple in Tirupati, points toward a resolution to this discrepancy:
Shuka, son of Vyasa received instructions in the supreme and sacred spiritual knowledge from kudra and became a Jnani while he was yet a boy. After perfecting himself, he conceived the entire Universe as Brahman, the Supreme Being. Mad with the knowledge, he wondered in the world. At the age of fifteen he shone with lustre like Lord Krishna. "Goddess Kamala is my mother. Lord Janardana is my father. Votaries of Vishnu are my relations. The three worlds are my native place" so saying Shuka once left his father - proceeded to the Sun. Finding his son nearing the Sun, Vyasa wept and shouted, "O my son, O my son." The Sun saw Shuka and said affectionately, "My dear boy, you have no sons. Go back to the Earth, head hanging downwards. Beget sons, get yourself redeemed of your debt and obligations to your parents and come here. One without sons cannot have salvation. Even if one performs Yagnas and does penance, a man with no sons is doomed. He can never reach heaven." Listening to the Sun's advice Shuka contemplated on Lord Janardana. He created another Shuka resembling himself head hanging downwards, and said "You are my son. Redeem my father from distress." and proceeded. The new Shuka then approached Vyasa who was lamenting for his son and learned Bhagavata. He married and had sons. By the grace of Lord Krishna, he became a Rishi.
My question is, what scriptures describe Shuka creating a duplicate of himself? As I discuss here, the Tirumala Sthala Purana consists of quotes from actual Puranas, so this story must be from one of the Puranas.
Srila Prabhupada discusses this duplicate Shuka story in this section of his commentary on the Srimad Bhagavatam:
The Śuka mentioned here is different from the Śukadeva Gosvāmī who spoke Śrīmad-Bhāgavatam. Śukadeva Gosvāmī, the son of Vyāsadeva, is described in great detail in the Brahma-vaivarta Purāṇa. There it is said that Vyāsadeva maintained the daughter of Jābāli as his wife and that after they performed penances together for many years, he placed his seed in her womb. The child remained in the womb of his mother for twelve years, and when the father asked the son to come out, the son replied that he would not come out unless he were completely liberated from the influence of māyā. Vyāsadeva then assured the child that he would not be influenced by māyā, but the child did not believe his father, for the father was still attached to his wife and children. Vyāsadeva then went to Dvārakā and informed the Personality of Godhead about his problem, and the Personality of Godhead, at Vyāsadeva’s request, went to Vyāsadeva’s cottage, where He assured the child in the womb that he would not be influenced by māyā. Thus assured, the child came out, but he immediately went away as a parivrājakācārya. When the father, very much aggrieved, began to follow his saintly boy, Śukadeva Gosvāmī, the boy created a duplicate Śukadeva, who later entered family life. Therefore, the śuka-kanyā, or daughter of Śukadeva, mentioned in this verse is the daughter of the duplicate or imitation Śukadeva. The original Śukadeva was a lifelong brahmacārī.
So the Brahma Vaivarta Purana may be a good place to look. Although I'm not sure if Srila Prabhupada is saying that the duplicate Shuka story is mentioned in the Brahma Vaivarta Purana or just that the story of Shuka refusing to leave his mother's womb is mentioned in the Brahma Vaivarta Purana.