I tried to access the entire alphabet succeeded by .com and I found out that only q.com and z.com are real websites. I did the same thing with the numbers from 0 to 9 and I found no website. Why? What would I have to do to own the a.com domain?
In 1993, the Internet Assigned Numbers Authority (IANA) explicitly reserved all single-letter and single-digit second-level domain names in the top-level domains com, net, and org, and grandfathered those that had already been assigned. In December 2005, ICANN considered auctioning these domains.
In a nutshell you can't own one as they are reserved and not available.