The Arudino IDE Support package also contains different bootloaders for quite a few variations of the Generation 7 Electronics RepRap controller board.

The Arudino IDE Support wiki page at the RepRap wiki also contains a paragraph on how to flash the bootloader onto the Gen7 board with avrdude. It suggest to write the fuses first, the flash the hex file onto the microcontroller and lock the bootloader afterwards. While there’s nothing wrong with that, it can be done in a single command:

$ avrdude -pm1284p -cstk500 -P/dev/ttyUSB0 \
-U lock:w:0x3F:m \
-U flash:w:bootloader-1284P-20MHz.hex \
-U lfuse:w:0xf7:m \
-U hfuse:w:0xdc:m \
-U efuse:w:0xfc:m \
-U lock:w:0x0F:m

Of course, the parameters regarding the processor and the programmer port may be different.

The actual bootloader hex files can be found in the Gen7 Arudino IDE Support package. Probably the easiest way to get it is to clone Traumflug‘s Gen7 git repository

$ git clone https://github.com/Traumflug/Generation_7_Electronics.git

The hex files can be found in: Generation_7_Electronics/arduino support/Gen7 Arduino IDE Support/Gen7/bootloaders/Gen7/

Make sure to choose the right one for your microcontroller and clock speed. The fuses for the different microcontrollers are listed in Generation_7_Electronics/arduino support/Gen7 Arduino IDE Support/Gen7/boards.txt