With the little I've learnt over the course of time, your a good Urls to generate down to dorks,from dorks to combos.
There's also Combo list of Hash and Combo list of Username and Password or Emails and Password.
E
well there is several ways if you mean HQ combos then you need to get good dorks and try get good URLs in SQLI there you get user:pass or email:pass depends on what you want
You would generally use leecher programs like x-slayer and then use (all in one checker - to filter emails) or obviously this forum and other forums as well, but you can do your own research.
I would appreciate it if you smash the like button if it helped