Not sure he's trying to get all of them in the same deck. Here's my suggestions, none-the-less: (hope you didn't want to keep it all water)
For Dark Blastoise, Furret's always a great choice to get those darkness energies on him quick. Also, if you can, get a metal energy or two on him. Back in the old days (last year), I had a great Dark Blastoise deck that used both metal and darkness. With a couple of metals on him, his was almost unhittable. I also like Dark Vaporeon with Dark Blastoise.
As for Octillery, anything that can poison is good to go with him, thanks to his suction cups. Cradily from Sandstorm would probably make a good comb with his own suction cups and lure poison. I've also played Base Gyarados with him to cause your opponent to have to flip every time to do a damaging attack.