Where can I get Tier 4 maps?

Hello,

I'm lvl 74 and I can't get to have tier 4 maps. Of course I could craft them by buying inferior tiers but I don't have enough money so what do I do?
I also refuse to do small tiers maps just to loot items and sell them to make money, it's too much time to lose
I could ofc buy them with my 6 exalts but I want to keep these to craft later
-> is there a flaw in the game or am I just bad at it?

Thanks

If you put a tier 3 waystone in a map that has corruption or irradiated it becomes tier 4.

You should craft your waystones to increase drop rate.
At least do transmutation, augmentation and regal. At higher tier you also want to use exalts.

The best way to get more higher tier waystones is to use your highest tier and best crafted waystone on maps that have bosses on them. (ideally bosses with irradiated and corruption).

Also in atlas passive tree get chance for higher tier and increased quantity of waystones.

Thank you for the corruption thing, I didn't know and will try it.