"Pure bred" is not what a lot of people think. No Rock is purebred, as it isn't a species like an eagle or sparrow. It is a composite of many birds at the time of their creation a hundred years ago. What makes a bird "exhibition quality" is not only it's health and cleanliness, but quite honestly it's spectacular display of it's being bred with the breed's Standard in mind.
The Standard fo the Barred Rock here in North America is different, slightly, than the standards set in the UK or Australia. Each poultry society in each nation sets it's own standard, a detailed description for the breed. Each part of the bird is carefully and exactly described. Shape being #1. Underline, topline, feathering, breast, legs, station on legs, tail, wings, neck, head, eyes and comb, just to name a few.
The odds of getting an exhibition quality bird from a breeder who essentially breeds for utility reasons is unlikely. However, you will have to grow out the bird and have it "judged" by an experienced eye. To breed for exhibition is a life long, complex endeavor. To get started, Google the breed clubs, the poultry clubs and societies in your state and country. Find a mentor. The internet is NOT the place to learn the ins and outs of fine breeding for the fancy.
Hope that helps.
The birds look rather nice. Yellow legs is a must for the breed. You'll find the legs turn much more yellow after they've spent time on grass.