As of now, the game is still listed on the legacy PS3 PlayStation Store. You can purchase it digitally and download it directly to your console.
on PS3 can be tricky because the game was a digital-only release on the PlayStation Network (PSN) and never received a physical disc version. Consequently, it typically exists in (package) format rather than a standard ISO dump. Reliable Sources & Methods According to community discussions on castlevania harmony of despair ps3 iso link
If you are looking for the game, here are the most reliable ways to access it without resorting to unofficial ISO links: As of now, the game is still listed