jackthom41:
Bootloader is not available in .hex file, the only way to install it is via Arduino IDE and the file used is avrdude.config as sometimes we need to change the signature in it while uplaoding bootloader.
If all you need is the standard 16MHz Arduino Uno and similar targets, a pre-built optiboot.hex file is available in the GitHub repo. Of course all the source and make files for creating any variant you may need are there as well in the root.
Pre-build AtMega328:
Optiboot root: