I was in your bout this week. My mp3 player is similar but a bit different. The keys were the same but the screen is smaller and it is 1gb.
To be honest with you i could not find a firmware for mine. You see i bout two of these players, so i had a spare one. What i did with the spare was i cloned the firmware and installed it on my broken one. The program i used was S1clonev13 which you can download from this address:
http://s1mp3.de/download.html#s1clone
If you dont have another working identical player what i sugest you do is download the program i mentioned and try to clone your firmware from your broken player. This is not going to fix it but whilst cloning your firmware you will get the microchips codes which will be extracted. This might increase your chanses in finding a firmware.
Goodluck dude. Hope you the best.