There are many Hindu organizations, and each of them has there own avatar! The ISKCON devotees consider Caitanya Mahaprabhu as an avatar. In what scripture do you find that your avatar's name is written?
Answer: What Scripture Doesn't?
We do not care for this organization or that organization. Nor do we care for any particular sect of religion such as Hinduism, Christianity, Judaism, or Islam. We simply care what the authoritative sastras and the great acharyas say.
Lord Caitanya's avatarship is directly or indirectly confirmed in practically every scripture in the world. Krishnadas Kaviraj Goswami, the author of Sri Caitanya-caritamrita, most emphatically stresses that Lord Caitanya Mahaprabhu is Sri Krishna Himself. He is not an expansion of the prakasa or vilasa forms of Sri Krishna. He is the svayam-rupa, Govinda. Apart from the relevant scriptural evidence forwarded by Srila Krishnadas Kaviraj Goswami, there are innumerable other scriptural statements regarding Lord Caitanya's being the Supreme Lord Himself.
For example to cite a few:
(1)From the Caitanya Upaniṣad (5):
gauraḥ sarvātmā mahā-puruṣo mahātmā mahā-yogī
tri-guṇātītaḥ sattva-rūpo bhaktiṁ loke kāśyati.
"Lord Gaura, who is the all-pervading Supersoul, the Supreme Personality of Godhead, appears as a great saint and powerful mystic who is above the three modes of nature and is the emblem of transcendental activity. He disseminates the cult of devotion throughout the world."
(2) From the Śvetāśvatara Upaniṣad (6.7 and 3.12):
tam īśvarāṇāṁ paramaṁ maheśvaraṁ
taṁ devatānāṁ paramaṁ ca daivatam
patiṁ patīnāṁ paramaṁ parastād
vidāma devaṁ bhuvaneśam īḍyam
"O Supreme Lord, You are the Supreme Maheśvara, the worshipable Deity of all the demigods and the Supreme Lord of all lords. You are the controller of all controllers, the Personality of Godhead, the Lord of everything worshipable."
mahān prabhur vai puruṣaḥ
su-nirmalām imāṁ prāptim
īśāno jyotir avyayaḥ
"The Supreme Personality of Godhead is Mahāprabhu, who disseminates transcendental enlightenment. Just to be in touch with Him is to be in contact with the indestructible brahmajyoti."
(3) From the Muṇḍaka Upaniṣad (3.1.3):
yadā paśyaḥ paśyate rukma-varṇaṁ
kartāram īśaṁ puruṣaṁ brahma-yonim
"One who sees that golden-colored Personality of Godhead, the Supreme Lord, the supreme actor, who is the source of the Supreme Brahman, is liberated."
(4) From Śrīmad-Bhāgavatam (11.5.33-34 and 7.9.38):
dhyeyaṁ sadā paribhava-ghnam abhīṣṭa-dohaṁ
tīrthāspadaṁ śiva-viriñci-nutaṁ śaraṇyam
vande mahā-puruṣa te caraṇāravindam
"We offer our respectful obeisances unto the lotus feet of Him, the Lord, upon whom one should always meditate. He destroys insults to His devotees. He removes the distresses of His devotees and satisfies their desires. He, the abode of all holy places and the shelter of all sages, is worshipable by Lord Shiva and Lord Brahmā. He is the boat of the demigods for crossing the ocean of birth and death."
dharmiṣṭha ārya-vacasā yad agād araṇyam
māyā-mṛgaṁ dayitayepsitam anvadhāvad
vande mahā-puruṣa te caraṇāravindam
"We offer our respectful obeisances unto the lotus feet of the Lord, upon whom one should always meditate. He left His householder life, leaving aside His eternal consort, whom even the denizens of heaven adore. He went into the forest to deliver the fallen souls, who are put into illusion by material energy."
itthaṁ nṛ-tiryag-ṛṣi-deva jhaṣāvatārair
lokān vibhāvayasi haṁsi jagat-pratīpān
dharmaṁ mahā-puruṣa pāsi yugānuvṛttaṁ
channaḥ kalau yad abhavas tri-yugo 'tha sa tvam
"My Lord, You kill all the enemies of the world in Your multifarious incarnations in the families of men, animals, demigods, ṛṣis, aquatics and so on. Thus You illuminate the worlds with transcendental knowledge. In the Age of Kali, O Mahāpuruṣa, You sometimes appear in a covered incarnation. Therefore You are known as Tri-yuga [one who appears in only
(5) From the Kṛṣṇa-yāmala-tantra:
puṇya-kṣetre nava-dvīpe bhaviṣyāmi śacī-sutaḥ.
"I shall appear in the holy land of Navadvīpa as the son of Śacī-devī."
(6) From the Vāyu Purāṇa:
kalau saṅkīrtanārambhe bhaviṣyāmi śacī-sutaḥ.
"In the Age of Kali when the saṅkīrtana movement is inaugurated, I shall descend as the son of Śacī-devī."
(7) From the Brahma-yāmala-tantra:
atha vāhaṁ dharādhāme
māyāyāṁ ca bhaviṣyāmi
"Sometimes I personally appear on the surface of the world in the garb of a devotee. Specifically, I appear as the son of Śacī in Kali-yuga to start the saṅkīrtana movement."
(8) From the Ananta-saṁhitā:
ya eva bhagavān kṛṣṇo
sṛṣṭy ādau sa jagan-nātho
gaura āsīn maheśvari
"The Supreme Person, Śrī Krishna Himself, who is the life of Śrī Rādhārāṇī and is the Lord of the universe in creation, maintenance and annihilation, appears as Gaura, O Maheśvarī."
And the list goes on and on....
Kindly take advantage of the mercy of Lord Caitanya. Join His most blissful movement of singing and dancing the names of God in great ecstasy.