Wouldn’t it be easy to make a normal map for your 3d model in Adobe Photoshop? I made this small action with accompanied styles for Adobe Photoshop to turn an image into a normal map. Download these files Lump CreateNormalmap, extract them and load them into Photoshop as shown in the images below.
Make a new document and draw something or load an existing image and run the action Lump_CreateNormalMap. Your image will be converted into a normal map with one dept. The action uses layer styles that can be adjusted if you would like to tweak the action. Maybe you have enough skills to make it work with different depths based on greyscales.
Best of all the action is FREE!
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Here is a video of the action at work:
https://youtu.be/KZXgRN52ioc