A good research university library will have period dictionaries, although that might be useful only for spot-checking certain words to make sure they're not anachronistic. The OED (Oxford English Dictionary) would be useful too because each entry usually includes historical usage notes, when the word entered the English language, etc. But if you're trying to establish an authentic-sounding 19th century voice, probably the best thing you can do is read, read, read from the period so that the flavor and tone and style will seep into your own writing. But you'll need to be careful about what kind of 19th-century English you want to be emulating. American and British authors, for example, differ widely. Expressions and vocabulary change from region to region, from social class to social class, and from year to year. In Europe, at least, the 19th century is a time of enormous change--political, economic, social--and these changes could be reflected in the language.
In another life I was a scholar of 19th-century French literature, and so I'm responding to you as an academic. I've never written historical fiction (though I have written scholarly, biographical articles). Just wanted to let you know where my two cents are coming from. Hopefully some folks with direct experience writing historical fiction will give you the benefit of their expertise!
Carolyn