Hi Alan,
If you want like you are saying "will receive new username and password"
Add the users as new users, just upload the account information using a csv leaving the password field blank. make sure that you choose Create password if needed. An email will be sent from Moodle with a new username and password. You may also have to allow email duplicates.
That being said. If the users are already in your LMS, why do you have to issue new usernames and passwords? Can you just add them to the new course site and post a News Forum topic that the course site is now available?