You can typically find this firmware through specialized technician forums or cloud drives. Note that many forums require a registration or a small fee to access the full archive split into parts (like part 8).
Some firmware archives for this specific board are shared via Public Google Drive links . Download SK706S PC822 3840x2160 REF71 part8 rar
The file you are looking for relates to the for the TP.SK706S.PC822 You can typically find this firmware through specialized
This technician forum hosts the USB Firmware for TP.SK706S.PC822 Download SK706S PC822 3840x2160 REF71 part8 rar