Infinite mountain height map

I’m working on a large exploration game that require a realistic world generation. I’ve tried fractale perlin noise but it isn’t enough good for me. What I need is a map that work a bit like Mathf.PerlinNoise (You enter the coordinate and it return the height/value). The result should look like what there’s in real life:
97294-mountain-height-map-merged.png
97295-mountain2-height-map-merged.png

I don’t want to use asset on the assets store to get want because the price is always high and the most of the time, the asset produce a map that is not infinite. Of course, I’m not going to wait for an awnser, just a clue or algorythm could help me reach my goal.

Check out this post, might have something that you’re looking for.