I don't have a go-to website, as this is not within my collecting range. I just remembered there were multiple sites with lists of known replicas. I also know there is a great variety of banknotes from that era, some issued by the Confederacy and others by state or local banks. Sometimes they were on the run as they shifted capitals and had to print money fast to finance the war effort - which is also why you can find authentic currency with blank backs

If you live in the South, there are lots of currency dealers who set up at coin shows or run their own shops. There's probably a book that has all the signatures, just as there are guides for U.S. currency. If you live in the North (as I do now) you're lucky to find one or two experts at major coin shows.