Not knowing your specific setup makes this pretty tricky … but here are some ideas for alternatives that might save you time:
Leave it as-is
If these authors aren’t actually users of the site to begin with, don’t change anything. Non-users shouldn’t be turned into users just for the sake of making search easier. Creating so many non-user user accounts will open up just that many potential entry points for malicious visitors.
Create a taxonomy
Again, assuming these authors aren’t actually users …
Create a custom “Authors” taxonomy and dump the author names in there. Taxonomical data is pretty easy to use in a theme to change styling, add attribution, etc. It also gives you archive pages and search functionality so you can index by author name.
The long way
If these authors absolutely do need to be turned into users … you’ve got a lot of work ahead of you. I’d recommend sitting down with phpMyAdmin and running some queries:
- Run a query to get a list of all author names
- For each author name, run a query to see if that author exists
- If the author doesn’t exist, run a query to create a dummy use for that author
Yes, it will take a while … but I’m hoping you don’t have 1,400 different authors for your 1,400 different posts. Your first query should return maybe 100 or so (hopefully you don’t really have 100 different authors!) results … that should definitely save you some time!