Hashes for all accounts (normal or extended) are stored in 'couch_users' (K_TBL_USERS) table. <cms:show k_extended_user_id /> should give you the record ID for querying the mentioned table.
Thanks, KK - having checked on my live site, that is indeed the case.
Oddly, my local copy of the site (with the database built in the standard way with an install_ex file) is missing all of the users in that table, except the superadmin user. I'd been trying this out on the local copy so as not to break anything important!
install_ex, by design, skips migrating users (the super-admin gets created automatically). I'd suggest you please use the mysql dump created by phpmyadmin as that will have the complete dataset.