It’s rare that I come up with a problem I can’t even Google, but googling “old-timey dictionary” just brings 1000s of dictionaries with the word entry “old-timey.”
I am looking for any books or online resources of antiquated and old-timey (see: old west/turn of the century) idioms, phrases, and terms. I vaguely recall on a The Simpsons DVD commentary someone discussing such a book they refer to for the antiquated terms Mr. Burns often use. I have found some Old English books but I’m looking for more like 1800s.
*A Classical Dictionary of the Vulgar Tongue * from 1811 is a fascinating source, though it’s specifically British English.
There are various old dictionaries at archive.org and you can find them in Google books, all public domain.
One trick I’ve found is to do a search for a word using Google Ngram viewer and then look for examples at the bottom. It will often lead you to public domain dictionaries.
Not what you’re looking for, but the Devil’s Dictionary is a fun read (for intellectualist values of “fun”) and, being a century or two old, it probably does feature a larger set of words that have died off over the years.
You might want to check out Passing English of the Victorian Era by James Redding Ware. It’s a dictionary of Victorian slang (mostly, but not exclusively, British) with very colourful explanations of the terms and their putative origins. You can see some examples in a recent quiz of mine from Babel: The Language Magazine: Vulgar Victorian Vocabulary (answers)
The Superior Person’s Book of Words and subsequent volumes by Peter Bowler contain many obscure words, including a lot of archaic or obsolete ones. In addition, they are quite funny.
I think the OP’s best strategy is just to read novels and plays from that era that represent the regional dialects they’re interested in, and use one of the many reference works suggested here to look up expressions that are unfamiliar. The best way to know how people’s language sounded in a certain period is to read dialogue that was written in that period (although of course written language doesn’t perfectly mirror spoken language).
A bit specialised in its focus on one book series:
A sea of words: a lexicon and companion to the complete seafaring tales of Patrick O’Brian
There are probably other historical dictionaries and guides for Sherlock Holmes, Jane Austin and other popular major writers which would contain a mixture of dictionaries with some of the specific language being used in the books, and broader discussion about the times and context of the stories.