As I discuss in this answer, the divine architect Tvashta (AKA Vishwakarma) created two powerful bows, the Pinaka bow for Shiva and the Sharanga bow for Vishnu. Brahma once got Vishnu and Shiva to fight each other to find out who was more powerful, and Vishnu won merely by saying the word "hum", as described in the Bala Kanda of the Ramayana:
Once, all the gods were asking the Grandparent, Brahma, as to who is powerful and who is less powerful among the blue-throated Shiva and Vishnu, but the Grandparent Brahma on inferring the intent of gods started to create adversity among those two, Shiva and Vishnu, for the Grandparent is the best adherer of truthfulness, as truth cannot be demonstrated on hearsay evidence. Owing to their animosity then occurred a fierce and hair-raising war among Shiva and Vishnu, as each aspired victory for himself. By the 'hum' sound of Vishnu that ruinously overpowering longbow of Shiva is [fatigued], and the triple-eyed God, Mahadeva, is frozen.
Then gods along with the assemblages of sages and celestial caranas have come together and appealed to those two for appeasement in the matter of wielding authority, and then those two superior gods, Shiva and Vishnu, went into a state of amity. On seeing the bow of Shiva rendered inert by the mettlesomeness of Vishnu, from then on the gods along with the assemblages of sages deemed Vishnu to be the paramount.
Afterwards Shiva's Pinaka bow was given to the king Devarata of Mithila, and it was passed down by the kings of Mithila until it came into the possession of Sita's father Janaka. It was the Pinaka bow that was famously broken by Vishnu's incarnation Rama to win Sita's hand in marriage.
But my question is about the Sharanga bow of Vishnu. Vishnu gave the Sharanga bow to the sage Richika, who gave it to his son Jamadagni, who gave it to his son Parashurama, another incarnation of Vishnu. Now when Parashurama found out that Rama had broken the Pinaka bow, he confronted Rama and demanded that he string the Sharanga bow. Rama was successful, and afterwards Rama gave the Sharanga bow to Varuna the ocean god, as described in a later chapter of the Bala Kanda of the Ramayana:
On the departure of Rama of Jamadagni, that most glorious Rama of Dasharatha is quietened at heart, and he gave away that longbow of Vishnu into the hand of inimitable Rain-god [Varuna].
But my question is, what happened to the Sharanga bow after Varuna got it? Krishna seems to have gotten it at some point; he used it, e.g. in his battle against the demon Shalva, as described in the Srimad Bhagavatam:
Śālva then managed to strike Lord Kṛṣṇa’s left arm, which held His bow Śārṅga, and, amazingly, Śārṅga fell from His hand.
So how did Krishna get the Sharanga bow? Did Varuna give him at some point? As I discuss in this answer, when Arjuna and Krishna helped Agni fight against Indra, Varuna did give Krishna two weapons of Vishnu, the Sudarshana Chakra and the Kaumodaki mace. But the chapter of the Adi Parva of the Mahabharata doesn't mention the Sharanga bow.