I learned to make pasta with semolina, but now I can't find it at the grocery store. Can I use Semola?

You ought to be able to. Semola is also durum wheat - just slightly more finely ground than semolina. It's actually more like what they use in Italy, I believe. If you use it though, because it is finer, you may find you need to use a different amount of water, but not very different.