Yes, Lord Indra can have 2 weapons of the same name.
Lord Indra fought with Lord Nandi in Daksha Yagna episode with Vajra. In Daksha Yagna sage Dadhichi was the one who cursed all the devas, etc for their sin of the Nir-Ishwara yagna.vSi, he was still alive.
Shiva Purana 18.104.22.168.:
- Indra fought with Nandin; the fire-god with Aśman and the powerful Kubera fought with Kūṣmāṇḍapati.
8-9. Nandin was hit hard by Indra with the thunderbolt that had a hundred spikes. Indra was hurt in the middle of his chest by Nandin with the trident.
Again, Lord Brahma told him to ask sage Dadhichi for his bone to make Vajra for killing Vrtra.
Shiva Purana 3.24.:
There is a great sage Dadhīci of great penance and of full control of his sense-organs. After propitiating Śiva he secured the boon of adamantine bones formerly.
You all request for his bones. He will undoubtedly give them to you. Make the thunderbolt staff therewith and kill Vṛtra without hesitation.
Let's see another example.:
Shiva Purana 3.23.:
- My discus is here. I shall take the discus and return to my region abiding by your order with reverence.
Nandīśvara said :-
On hearing the words of Viṣṇu, lord Śiva the protector of virtue in the guise of a bull, replied to Viṣṇu again.
You shall go away quickly from this place. You shall not delay, O Viṣṇu, this is my behest. Let your discus stay in this world itself.
I shall give you a discus more terrible than the sun at the time of dissolution and more efficacious than the words of Śiva.
After saying this Śiva created another blazing discus, as lustrous as the Kāla fire, for the destruction of the wicked.
He gave the discus, as lustruous as ten thousand fierce suns, to Viṣṇu, the great Ātman, the protector of the gods and the leading sages.
Here, in Linga Purana interestingly the events if both Shiva Purana and Vishnu Purana are joined. So, 1st Lord Vishnu got Sudarshan Chakra from Vishwakarma which was made up of Sun particles than after it got blunt due to the Hard bone of sage Dadhichi he got another one from Bhagawan Shiva which was created to kill Jalandhara.
Linga Purana 1.98.:
11-15. Since they have acquired boons, they cannot be killed with any of these arrows and miraculous weapons:—such as those belonging to Viṣṇu, Brahmā, Rudra, Yama, Kubera, Soma, Nirṛti, Varuṇa, Vāyu, Agni, Varṣa, Sun, Īśāna, and other terrible missiles which make others tremble and powerless. O lotus-eyed one, all of them defy death due to their boons. O preceptor of the universe, the blazing Cakra (discus) that belongs to you, and that has originated from the solar disc has been rendered blunt by Dadhīca, son of Cyavana. Your staff and bow, your miraculous weapons have been acquired by Daityas through your grace. Formerly, a terrible and sharp-pointed discus was evolved by lord Śiva, the enemy of the Tripuras in order to kill Jalandhara. It behoves you to kill them with that weapon.
So, from the above examples we can understand that a deity can also have an upgraded version of the same weapon with the same name and functions but just better.
So, Yes, There are 2 Vijaya Bows in Mahabharata.
Bow of Rukmi.:
And Rukmi was a disciple of that lion among the Kimpurushas who was known by the name of Drona, having his abode on the mountains of Gandhamadana. And he had learnt from his preceptor the whole science of weapons with its four divisions. And that mighty-armed warrior had obtained also the bow named Vijaya of celestial workmanship, belonging to the great Indra, and which was equal to Gandiva in energy and to also Sarnga (held by Krishna).
Udyoga Parva: Section CLXI.
Bow of Karna.:
My (Karn’s) bow, called Vijaya, is the foremost of all weapons (of its kind). Desirous of doing what was agreeable (to Indra), it was made by Vishakarman (the celestial artificer) for Indra. With that bow, O king, Indra had vanquished the Daityas. At its twang the Daityas beheld the ten points to be empty. That bow, respected by all, Sakra gave to Bhrigu's son (Rama). That celestial and foremost of bows Bhrigu's son gave to me. With that bow I will contend in battle with the mighty-armed Arjuna, that foremost of victorious warriors, like Indra fighting with the assembled Daityas. That formidable bow, the gift of Rama, is superior to Gandiva. It was with that bow that the Earth was subjugated thrice seven times (by Bhrigu's son). With that bow given to me by Rama I will contend in battle with the son of Pandu. I will, O Duryodhana, gladden thee today with thy friends, by slaying in battle that hero, viz., Arjuna, that foremost of conquerors.
Karna Parva: Section 31.
Karna's words are also backed by Brahmanda Purana.:
He (Lord Shiva) gave an unaging (ever-new) unbreakable divine bow (named) Vijaya, with firm bow string, with firm bow string. He gave him (Parshurāma) a costly wonderful coat of mail that could withstand all types of weapons. (Brahmanda Purana_2,:25.41).
He (Vratya/Shiva) is the only (Ekā) ruler of the Vratya group, The bow which was touched (held) by him was called Indradhanush. (A.V. 15.1.6).
So, from above verses it's totally clear that there were two Vijaya Bows of Lord Indra but one was better than the other. As.:
Rukmi's Vijaya Bow = Gandhiva = Sharanga.
Karna's Vijaya Bow > Gandhiva.
Therefore, Karna's Vijaya Bow > Rukmi's Vijaya Bow.
I hope this clarifies all your queries. Prd..