Or check the lists of other users who've already spent the time and effort creating and editing them and follow entire lists! (lawyerist.com)
You can download entire lists of known pairs, and there's even the appropriately named web site RouterPasswords where you can look up just about any make, model, and default login. (howtogeek.com)
Hopefully will get a deal out of my first group of mailings, but I know that May not be realistic and will follow up on entire list. (biggerpockets.com)