In the merchant resource section there are stitches you can add in photoshop to the texture. There are photoshop brushes that let you paint stitching onto the model's UV maps. I suppose how you unwrap the object for UV mapping would be important so You can paint your stitches and line them up. There are Stitch kits and a tutorial on how to make the stitches look real so they are not just colored dash but have dodge and burn to add depth of shadows and such. So yeah, I'm sending you to the marketplace. The products might be dated, the method might be dated, its the only one I know of. Perhaps Marvelous Designer does this, but I can't afford it so I wouldn't know.