I am looking for a mod that would act like the IRS and help fight tax evasion while allowing me to keep my taxes up
I think that the various taxes assume collection and auditing agencies. The point at which tax evasion becomes a problem is the turning point where additional enforcement would cost as much as or more than the additional taxes collected.
However, it would be interesting to allow a player to squeeze his people harder and suffer both the cost of enforcement plus the flight of capital (negative GDP) as people with money move it to other countries or just bury their money under mattresses.
Of course, a government could probably eventually lock the borders and overcome any unwillingness of people to pay, but then the country would be no more democratic than a so-called democratic people’s republic of .
I suppose it would be really simple to add a Tax Collection Agency policy.
For a cost it would obviously reduce tax evasion. It should probably reduce the happiness of many groups, possibly even that critical “Everybody” group. It could also give a small happiness boost to capitalists.
Some increases to areas like Poverty or Equality could also occur, but the increase in taxes this allows negates the need for high amounts of it.