A few people have been interested in building padded arm rests.
It’s not very hard, just start with a core framework for the shape you desire. This is usually just a 30 to 40 degree bevel frame. This can either be attached directly to the the edge of the bar or supported with wood brackets made from 1 x 4 pine material painted black. The bracket approach will give you an arm rail that is in a slightly lower but in a more natural position.
Here’s a photo from the gallery:
Framework profile – https://www.barplan.com/gallery/displayimage.php?pid=40&fullsize=1
Framework covering – https://www.barplan.com/gallery/displayimage.php?pid=44&fullsize=1
Another example of padded arm rail using the support bracket approach – https://www.barplan.com/gallery/displayimage.php?album=9&pid=3106#top_display_media
Once your frame is built, you will cover the arm rail sections with foam, stapling from behind, then cover with your choice of material, stapling from behind. You may want to build a sample section to practice because stretching the fabric properly is a skill that must be tried a few times before you get it just right for your specific rail shape.
You can get the foam & vinyl leather materials from any sewing fabric center.