Wrote this little python script in about 1 hour with @133spider. Dumps about 8000 usernames (every user from every guild on the Guild Launch website) in just a few minutes. Could make it faster with threads but it's not really necessary since it takes so little time anyways.
Select 1 for the input for it to scrape, was too lazy to implement it the other way. If you know of any other websites that hold a lot of username data that you want scraped lemme know.
This will return the same thing every time unless people create new guilds or join existing ones.