The Tax Collectors in Revelation are pretty much the same as the Borgia Couriers in Brotherhood.
As soon as you see this small red purse on your mini map...
Image credit to
TheFlyingToaster / BreadSkin on PlaystationTrophies.org
...chase after him. They are quite fast and nimble. Simply get close and then tackle him with

while sprinting.
Might take quite a bit of time to actually encounter one. I saw my first one in Sequence 4 on the southern edge of map.