To answer the main question, why is it hard to find "real slim shirts", it is because as stated in a lot of articles and in a lot of news recently, most people are obese in America. Companies want to sell to most people so they make big shirts.
I "feel your pain" because I am 6,4 inches and 165 lbs. No freaking shirt will fit me properly. We have 1 store that is called Mexx in Canada that will sell decent shirts (at least for the size) but still, far from perfect.
The shirts that the models wear on your pictures are very adjusted. I own 2 bespoke shirts that are like that (just half an inch more lose) and it is not hard to wear, I am not constricted in them, I and I look good in them.
Do yourself a favor and get some bespoke shirts!