Declension table of ?vivastra

Neuter	Singular	Dual	Plural
Nominative	vivastram	vivastre	vivastrāṇi
Vocative	vivastra	vivastre	vivastrāṇi
Accusative	vivastram	vivastre	vivastrāṇi
Instrumental	vivastreṇa	vivastrābhyām	vivastraiḥ
Dative	vivastrāya	vivastrābhyām	vivastrebhyaḥ
Ablative	vivastrāt	vivastrābhyām	vivastrebhyaḥ
Genitive	vivastrasya	vivastrayoḥ	vivastrāṇām
Locative	vivastre	vivastrayoḥ	vivastreṣu

Compound vivastra -

Adverb -vivastram -vivastrāt