Any one or two letter domains that you can find are shown as "Availiable" as they are reserved because you can no longer renew domain names that are less than 3 letters.
The only way of you actually getting these domain names is by buying them of someone that has an active 1 or 2 letter domain name. They are dormant once they expire.
And lets just face it, If there is no way of getting domains of 3 letters without advance technology... then there is no way that if one and 2 letter domains were allowed that there would actually be some avaliable!
Hope this answers your question.
- LuKe :D