Where can I find a tax collector to kill for Tax Evasion?

I found one running around randomly, but I've only seen one, period. They show up like the Borgia Messenger does in previous games, the icon looks like a red money bag.

Over on this thread is a supposedly repeatable way of getting one to spawn, by hiding near the Hagia Sophia tunnel entrance and waiting for a particular bank deposit in the day cycle, when one will almost always spawn.

Here's the related video:

From what I have read, it seems to be easiest to find a tax collector if you are near a bank when the deposits come in. That seems to be when they are most likely to appear.