... some possible real solutions to this growing problem, and they all amount to making it harder to obtain a gun

If you succeed in making it harder for law-abiding U.S. citizens to obtain firearms, you will ultimately make it easier for non-law-abiding U.S. residents to obtain firearms.

You are correct about the U.S. being unique with respect to the 2nd Amendment. What works in the Netherlands will not work in the U.S.

Just look at the volume of gun sales in the U.S. under every democrat president over the past 30 years. Whenever a democrat president gets in office and pushes rhetoric about trying to "[make] it harder to obtain a gun," gun sales skyrocket.

Why is this? Because there is a LARGE group of Americans who believe the 2nd Amendment is FUNDAMENTAL to freedom from tyranny in this country. You can disagree with their logic and their philosophy, but you cannot deny that they exist and that they firmly believe 2A = Freedom from Tyranny.

As such, any substantive curtailment of their 2nd Amendment rights will lead to a large increase in the number of black market gun dealers. An increase in the number of black market gun dealers will simply make it easier for those who are currently forbidden from purchasing firearms to do so (e.g those who have been adjudicated as mentally ill, convicted felons, substance abusers, minors, those convicted of domestic violence, etc.).

The net effect will be similar to what happened during prohibition. Millions of otherwise-law-abiding Americans (i.e. those who believed they had a 'right' to consume alcohol) were forced to purchase their alcohol through illegal channels. This led to an explosion in organized crime. The problem was, once prohibition was reversed, those crime families did not simply go away, they merely shifted their focus to other forms of illegal activity (or just kept producing and distributing illegal alcohol, circumventing government oversight, taxes, etc.).

Even something seemingly innocuous, such as requiring universal background checks for all firearms purchases, will probably backfire and lead to an increase in black market activity. However, I have devised an alternative to a 'universal background check' system that would accomplish the same intent without the likelihood of increasing the number of black-market channels. I will try to publish a post about that in the next week or two.