The GBA doesn't have a BIOS; you're thinking of ROMs (effectively, the cartridge contents dumped to a file). ROMs are covered by copyright, and are indeed illegal to distribute without authorized consent (which Nintendo would never give). However, there are homebrew ROMs you can legally download and distribute. No emulator I know of, including this one, illegally ships with (or describes how to illegally obtain) copyright-protected ROMs.
The GBA does in fact have a bios, but modern emulators do not require it except for some rare edge cases that their reverse engineered bios can't handle.
Can you provide any info on this? I'd like to know more, it sounds interesting.