I'm trying to find information on the extinct names. My ideal goal would be any kind of list of surnames in use prior to the 15th century AD (or CE, whichever you prefer), including surnames that no longer exist. (It's easy to find which surnames still exist, so a simple process of elimination can be used on a complete list.)
It's very easy to find lists of the common names, relatively easy to find lists of the less common names; no luck at all finding information on extinct names.
Google searches have included: extinct names, extinct surnames, extinct Korean surnames (also lost surnames, dead surnames, surname attrition, daughtering out, vanished surnames), Korean surnames, and a lot of ancillary searches on early Korean history and Korean culture. I found a link to a site purporting to have a list "including vanished surnames", but the site is in Korean.