I'm fairly sure if you extended the list to idk, 1000 or 10.000 you'd see all two/three letter domains being taken. Same with e.g. Twitter accounts. You might still have a chance with your local Slack team though.
First you had to know what the internet was.
There was a massive wave of domain-squatting round about 2000 in the dotcom boom, and as a result "trademark reform" was enacted to allow brands to confiscate their named domains from domain squatters.
Also, quite a lot of domains had specific requirements. You either had to be in the country, or a specific kind of business, or know the sysadmin running the registry personally.
[EDIT: Duh. Of course, it was actually Class A blocks at the time.]
Maybe a little out of date by now, but still, you can get a feel for it.
Apple, Ford, HP, DEC, Xerox, among others all have full /8 blocks.
Are you implying that they were printed out, individually packaged, and offered in a bowl?
Big mistake that was..........
I remember having a two-digit handle with InterNIC, too bad that wasn't worth anything. =)