Well, leather is basically skin. Learn to paint skin. If you are trying to airbrush skin to the point of having hyperrealistic texture you need stencils. Make them by scraping small holes in paper. If you don’t know the basics of matching color then you have a loong way to go.
Airbrush academy has some nice stuff on youtube. IDK if they have anything on skin.
Check out my work in the acrylics Hall of Fame Camellia WIP
oil and acrylic paintings..