In March of 2008, I did a little experiment where I conducted a random sample of the LLLLL.com space (5 letter .com domains). What I found was that approximately 89.2% were unregistered, meaning that out of a total field of 11,881,376, approximately 10.6 million were available to register. My random sample had a margin of error of 1.79% (sample size = 3,000).
The fact that 10% of these domains were registered was somewhat shocking, given that nowhere close to that many could be pronouncable or actual words. There were some jokes on the forums in 2008 about an "LLLLL.com buyout", given the buyout frenzy following the LLLL.com buyout. Hopefully nobody went and tried to register these on the hopes that there would be a buyout.
Today, being curious, I reran a random sampling of the LLLLL.com space. I used a random character generator function in excel to produce 5 random letters, 500 times (a great function: "=CHAR(INT(RAND()*26)+65)"). And then I used Godaddy's bulk checker 6 times to sample 3,000 random LLLLL.com domains.
The random sample showed that approximately 87.8% were available to register, a drop from 2008 but not outside the margin of error so it's hard to lend much significance to the results. With this percentage, there should be approximately 10.4 million available to register.
However, with the increasing registration of .com domains in general, and the greater international presence on the internet (i.e., more demand for unusual spellings/words), it seems likely that more LLLLL.com's have been registered since 2008. Just not enough to get close to a countdown...
To search for random NNNNN.com's, you need to use a random number generator function (=RANDBETWEEN(0,99999)). Then you need to select "format cells" and select "special" and then "zip code". This makes sure that 5837 shows up as 05837 so you can search for the NNNNN.com instead of an NNNN.com (which we know is already gone).