Muse Communication holds rights to many anime in Southeast Asia and India. They have released Digimon movies and series, though check their playlist for Frontier specifically.
Amazon Prime occasionally licenses older Digimon seasons. As of now, they have Digimon Adventure and 02, but keep checking their anime catalog for Frontier. They do offer Hindi audio for some seasons. Digimon Frontier Hindi Episodes Download -
Most fans rely on fan-uploaded episodes. These are not legal, but for personal/archival use, here are typical sources: Muse Communication holds rights to many anime in