After trying several solutions, and after waiting far too long for the collector, I found the following solution that worked for me on the first try. This guide comes from a comment on Achievement Hunter : http://achievementhunter.com/games/comments.php?id=83308
"1) Wait at east of arsenal where the riot started with the bank that there renovated
2) Withdraw any money from the bank and then wait by the entrance to the arsenal
3) When it pops up saying money has been deposited into the bank take few steps into the arsenal
4) Boom the tax collector spawns and all you need to do is chase him down "