I don’t keep track of them. 🙂
I solicit PMs from people, to let me know who’s been banned or blocked.
Or deactivated. In fact, deactivations really do require me to keep track of people, because I try not to report deactivations immediately—usually people come back on Quora shortly afterwards. I fail to keep track of deactivations, and I ask people to get back to me if the user is still deactivated after a couple of days. (Hence me giving lots of people a fright, by reporting User’s deactivation as early as I did.)
More to the point, I’m amazed how the people who regularly report bans and blocks keep track of them. I add in reports when I notice them, but I don’t notice them nearly as often as my regular reporters do.
I also subscribe to the Quora Account Suspension and Bans topic, so I will get news of some “Why was X banned?” questions before they are deleted. But PMs are far and away the main source of information.