With any luck the secondary source authors will tell you what primary sources they used, which will make your job easier.
21st Century: The most current print guides are in the Reference department (4th floor, Wilson Wing) with the very newest ones behind the Reference desk. Call numbers: PE1407-1460.
Also try searching the ZSR home page search for your rule and then limiting the results to Reference to find entries within online reference books.
20th Century: Look in the Main Stacks (5th floor, Reynolds Wing) in call numbers PE1407-1460. Some guides are scattered in other places, so check the ZSR Catalog if you have a specific title in mind.
19th Century: Check An annotated bibliography of nineteenth-century grammars of English particularly starting on p. 378 "Advice on good English." Once you have a title, you can usually find the full text in Google Books.
16th-18th Century: If you identify an older title of interest, you can usually find an online copy via the ZSR Catalog. (The bibliography of 19th century works mentioned above lists some 18th century examples starting on p. 357.)
Oxford English Dictionary
The OED attempts to find the oldest use of each sense of a word.
Pay attention to when the OED entry was updated! Compare the entries for hopefully and literally. We have older printed editions of the OED if you need to compare them. (Second edition. First edition.)