Firmware for kw-pc1002c tablet

I have a kw-pc1002c tablet (10".1,rk3066 1.5 Ghz 1 GB Ram,touch screen gsl3680,wifi rk903,
Android 4.1.1 JB) manufactured by Kinwei Technology Co. , the bootloader doesn't work.
I- I need a compatible or original stock ROM to flash on this device.
II- When it worked ,this tablet suffer from poor WiFi performance.
How i can later update the ROM with a different WiFi driver version?

Thanks for any answers.