thats good going KS. you'll find that the better time is not only a result of training but also motivation.
im wondering how your shin splints are going. have you had any pain? whata re you doing to prevent them?
here's some calf exercises. there isnt a massive range of calf exercises, but theres about half a dozen here that you could do.
Calf Exercises - Training & Workouts For Huge Calves!
However, since shin splints are linked to tight calf muscles, i think you should be careful that you dont train them too hard one day and go out for a hard run the next day with tight calves.
i personally think you dont need to do calf muscle exercises because you train them when you run with every step. I think in the gym you need to concentrate on core musle strength, as well as working your glutes. The glutes are forgotten muscle group that keep your body aligned and gives you drive. I found some useful glute exercises that im going to start doing myself on the Runner's World website the other day.
Glute Strengthening Workout From Runner's World