Actually, the calves are comprised of the soleus and the gastroc. I believe it was the soleus that was mainly made up of slow-twitch fibers, while the gastroc had fast-twitch. Typically, both fiber types are hit, but calves are a rare, very stubborn case. This is why in another thread that we had on this (what, two fucking weeks ago?) I posted something very simple to do for calves. 3-4 sets of a standing heel raise for 6-8 reps, then 2-3 sets of seated heel raises for 10-12 reps. Give that a shot, and just try and progress like anything else. The calves should grow.
And I'm sorry, but squats really don't give you bigger calves. They barely come into play in the squat. Maybe isometrically, but dynamically? Nah-uh. People assume that PLers have big calves because they squat big. They get big calves because they get very heavy and any walking becomes a workout. If you weigh a lot, you're going to have some minor calf growth over time.
Of course, I'm in agreement with mek 100% - sprint. Sprints are so anabolic for the lower body if you run properly. And get this notion out of your head that cardio is going to slow down muscle gains. First off, sprints should be treated as a lower body workout in and of themselves, and second, you just need to eat enough to grow. Eat enough calories to compensate for your activity, and guess what? You're still going to grow.
Now I can make a case for an excessive amount of cardio (think jkurz) getting in the way of muscle gains, but there are other things that come into play.