Currently, the only captain's class that is available is through XGC Tommygun XD; he runs them on both CoD4 and Halo 3, alternating each week at I believe 3:00 PM EST, but I'm not for sure on the exact time. The best way to get in touch with him would be through PMs, although you might have just as much luck if you just sent him a message via your gamer tag.
-Ashley