With the earliest text below (Toh597/984) the Ushnishavijaya Dharani is taught by Shakyamuni Buddha to the Chief of Gods Indra (Shakra). The following four texts known as the 'Kalpa' category of Ushnishavijaya literature have the dharani taught by Amitayus Buddha to Avalokiteshvara while in the Western Paradise of Sukhavati. This could very well be another conflation between Amitabha Buddha and Amitayus.
8/9th Century: Toh 597/984. The Incantation of Uṣṇīṣavijayā. གཙུག་ཏོར་རྣམ་པར་རྒྱལ་བའི་གཟུངས། · gtsug tor rnam par rgyal ba'i gzungs. sarvadurgatipariśodhany uṣṇīṣavijayānāmadhāraṇī. [10 pages]. ([Shakyamuni Buddha] Jinamitra, Surendrabodhi and Bande Yeshe De)
Toh 596. The Incantation and Practice of Uṣṇīṣavijayā. གཙུག་ཏོར་རྣམ་རྒྱལ་གྱི་གཟུངས་རྟོག་པ། · gtsug tor rnam rgyal gyi gzungs rtog pa. uṣṇīṣavijayādhāraṇī kalpasahitā. [4 pages]. ([Amitayus Buddha] Translators?)
11th Century: Toh 594. The Incantation and Practice of Uṣṇīṣavijayā. གཙུག་ཏོར་རྣམ་རྒྱལ་གྱི་གཟུངས་རྟོག་ · gtsug tor rnam rgyal gyi gzungs rtog. uṣṇīṣavijayādhāraṇī kalpasahitā. [16 pages]. ([Amitayus Buddha] Dharmasena & Khampa Lotsawa Bari Rinchen Drag)
Toh 595. The Incantation and Practice of Uṣṇīṣavijayā. གཙུག་ཏོར་རྣམ་རྒྱལ་གྱི་གཟུངས་རྟོག་པ་དང་བཅས་པ། · gtsug tor rnam rgyal gyi gzungs rtog pa dang bcas pa. uṣṇīṣavijayādhāraṇī kalpasahitā. [10 pages]. ([Amitayus Buddha] Translators?)
11-13th Century: Toh 598. The Practice of the Incantation of Uṣṇīṣavijayā. གཙུག་ཏོར་རྣམ་རྒྱལ་མའི་གཟུངས་ཀྱི་རྟོག་པ། · gtsug tor rnam rgyal ma'i gzungs kyi rtog pa. uṣṇīṣavijayādhāraṇīkalpa. [5 pages]. ([Amitayus Buddha] Lotsawa Neten Palkyi Nyima Gyaltsen Sangpo & Ne'u Khenpo)(The images below are only a selection of examples from the links above).