Is there a national Registry of Expired Patents that one can search through for reference?
Yes, there is a list. No, it is not exhaustive. In fact, the patent system is expressly designed for this purpose. We want people to know about expired patents and to use them as they see fit. The USPTO Patent Database provides patent images for all patents since 1970, and text files for all patents since 1976. Every patent issued before 4/10/2000 (as of this writing) is expired. Some patents after that date are expired, depending on whether the patent has been abandoned. There is no list of every single expired patent, but you can produce a list of the bulk of expired patents, and then search more recent ones on a case-by-case basis as necessary.