Your best path is clear: source the Greek Blu-ray, create your own digital copy, and host it on a private media server. Barring that, seek out verified 1080p MKV releases from Greek tracker communities. Avoid streaming sites promising "Greek high quality" – they almost always deliver low-bitrate, censored garbage.
As for the film's online availability in Greek with high quality, there are several options. The film is available on various online platforms, including streaming services and video-on-demand websites. Some popular options include: a serbian film online greek high quality