I'm not sure if this is what you are asking, but I'll take a stab at this. The word "bald" is an adjective, describing a noun (he is bald; he is bald headed). In adding "-ly", the word turns into an adverb. As adverbs tell us, in general, how something is done, it doesn't make sense to say "He baldly scratched his head."
Bold/boldy makes sense. He is very bold (adjective) when he stands up to the teacher.. He boldy stood up to the teacher.
Bald is pronounced the same as the word "all" or "awl": bawld
Bold is pronounced the same as the word old: bohld
Bald and baldly are related, aren't they? It would help if you explained what you meant. "Bald" means "hairless," but it can also mean something like "unadorned." Its adverbial sense is almost exclusively based on this second, less common definition.
I see why they were not related to me at the beginning. In the English-Spanish translation for "bald" it is not given the third connotation of it, which is listed in the English-English dictionary, provably the one with the related meaning to "baldly."
Let me post the question in the Spanish-English forum to see what comes of it.