Hi, have you thought about making the same brushes for Affinity?
Viewing post in Wuggy's Classic Cartography Set comments
Affinity seems to support ABR files, so no separate files are needed: https://www.affinity.studio/help/panels-brushes-panel/
Here you will find instructions on importing brushes to Affinity: https://www.affinity.studio/help/addons-importing-addons/
(This is for the new Affinity Studio, I have not checked if the same applies to Affinity v2)
I tested today. I was able to import the ABR to Affinity Photo v2 using the normal Import brushes feature and they work with the brush tool.
Instructions: Open Brushes-panel > Panel menu > Import brushes > Select the ABR file you want to import (you'll need to unzip the downloaded zip archive first).