If you are ICANN accredited and have a contract with the Registry, or make a deal with an ICANN accredited Registarar, then you can use the RRP protocol and directly query the Registry servers.
Some reseller accounts let you query in real time using scripts as well - however high volume queries are discouraged against the "user" queues, so you'll need one with a batch queue that allows high volume queries to pick up dropping domains this way.
If you look at the list of ICANN accredited Registrars - many of them don't even offer public domain registration services...
ICANN frowns on that practice, hero. Apparently, they are, or have, cracked down on that practice. But with all the corrupt registrars around today and Lyn Stuart resigning, there are probably plenty hidden in rat holes out there who could crawl out of the soil.
Someone please email or PM me with this information if you aren't willing to post it on the forum. I tried to sign up for club d but I get no responce from anyone about it nor does anyone seem to give much information about this in the forums.