Yesterday I found a 3-year old opensource project for typing old Hangul. Of course, I forked & modified it!

Now available: the Pilipino Hangeul online keyboard!

삐ᄙᅵ삐너 한글 (Pilipino Hangeul) IME

Philippines Pilipinas Filipino 삐ᄙᅵ삐너 한글 FLOSS FOSS YourOnlyOne