Well, i think you can still get Dark Knight and Samaurai from where you are now, but you'd need to go up to the surface to get them. Samurai is in Kilika Temple, and Drak Knigth is in Bevelle, there's a huge thread on the forums here about getting it, follow that to get it when your inside, though I'm not sure if you can get it from where you are. It's useful against Final-Boss-Dude-Guy-That-I-Can't-Remember-The-Name-Of becasue it has many parts. If you need anymore help, you know who to call!