You may or may not know, but there only some of the foreclosures are actually being listed by the banks at any given time. The banks only list a portion of them at a time, and the reason is simple economics.
If the banks were to unleash to all the foreclosures back on the market once they become REO it would create a huge amount of supply, further driving down prices of homes - homes which they need to sell for as much as possible to recover their losses on the mortgage.
Also, some banks - even though they have gone through the foreclosure process on the home - they keep the property in the names of the previous owners to avoid the HOA and other fees (the legality of this was taken up in court recently). So even lists compiling county data quite regularly will be missing these by my understanding.
Just because a bank isn't actively listing a house with a agent or on MLS, doesn't mean the bank is not willing or does not want to sell it. It just means they aren't putting it out there to the masses to keep from further softening the prices.
This is why contacting banks directly can provide you with access to more properties others are not aware of. Now, some banks will simply hold those "secret" properties no matter what until they are ready, but some will.
This leads to my point about being creative when it comes to finding foreclosures, since many aren't listed or on foreclosure lists.
One way, be sheer accident, I was able to uncover a foreclosure in my area which was a ghost to the foreclosure lists, MLS and other real estate resources was using Bing Maps (formally Live Earth - by MSN). Now, you could use Google Maps/Earth, or Yahoo Maps... any map site so long as it has satellite (bird eye) images. I prefer Bing because they have better images that zoom closer/clearer, and you can also rotate the perspective on them.
So how did a aerial photo allow me to identify a string of foreclosures (with a couple undocumented ones = no competition)? When researching a possible deal I was scanning the neighborhood. To my surprise, I saw a drained pool, and then another, and another - all just a couple houses apart.
In my part of the world, the only time a pool is drained is if it needs repaired or it is a vacant house. The odds of 7 houses out of a cluster of about 100 having pool repairs done, or for some odd reason just opting to have a dangerous hole taking up most of their backyard is quite low.
A couple showed up on foreclosure lists, but the rest didn't. I could further verify the houses were likely vacant because the lawns were dying.
The next step? Look up the property in the county records and see who owns that property now and try to get in touch with someone who can authorize a deal on the property.
This doesn't mean they will bite at a low offer from someone who found one of their "secret" foreclosures... but this does illustrate there a lot more foreclosures than meet the eye, and getting creative in your methods can give you opportunities that give you an edge over anyone else.
In the end, your edge is what makes you money - whether it is assignment, flipping, rentals/cashflow... it doesn't matter. So always keep looking for ways to increase your edge through creative techniques.