Got a fake Samsung Galaxy Grand Duos and you need the firmware, its right here. Like seriously, this Samsung I9082 clone with an MT6577 MediaTek processor hidden inside is so identical to the original I9082.
It even enters a fake download mode like other Samsung Android devices. But, Odin will never find it. You can figure out its real id via ADB or be using an app that displays in-depth phone info e.g CPU-Z.
If you happen to purchase this very popular cloned Samsung I9082 and encounter issues related to your firmware, you can download this ROM and flash it using the tutorial.
Note: Make sure your device is the same as mentioned above before flashing the firmware. Flashing this I9082 cloned ROM on anything other than the device will actually render it useless.