I am learning Hangeul and found this image on the Internet (I cannot locate the original source):
It seems like some of the syllable blocks are greyed out, which I think means it's not used. There's a thread on HiNative which seems to suggests they are not used unless it's for onomatopoeia. I also searched for these characters on Naver Dictionary, and it looks like there are usage but very limited:
Why do these specific sounds (댜 뱌 챠 탸 퍄 햐 됴 툐) not exist in normal vocabulary? Is it for historical reasons? Perhaps because these sounds don't exists in Hanja (classical Chinese)?