It took me ages to come up with a way that worked for me. These Brockhaus scans have been sitting on my HD forever, and I couldn't find a way to replicate this irregular hatching for the borders (or the sea).

(Note to all: if someone would present a simpler way than I finally did... don't be shy!)

So this is what I did:
The base texture for the borders is rendered in Blender. Basically it is a striped (wave: band) texture, slightly distorted and modified with some noise, then rendered to the size I needed.

Click image for larger version.  Name: workflow1.jpg  Views: 254  Size: 198.3 KB  ID: 55925

In my current work, I already merged down the outer narrow borders and the inner striped borders, so that I cannot colourize them independently any more. That was really really stupid.

But you always learn something, don't you?