When you're in the fabric paint/wood paint aisle, read the backs of the paint bottles to see if you can use it on leather. I'm thinking that maybe the paints in the woodcrafting aisle or the ceramic/wall stenciling aisles of any craft store would have something. Worse comes to worse, grab one of those roaming people with the aprons and demand they tell you where to find such paint.
For a sealer/top coat, look in the fine arts section. It'd be in an aerosol can. Again, read the back and see which one will work for you. I've used one of those on a plastic-y surface before (slightly flexible) and it worked just fine.
Hope this helps!