Your best bet for obtaining BHPL/Ribbon armor is, indeed, Dark Yojimbo since you can fight him 4 times in a row then repeat. If he doesn't drop the armor you want, his common item drop (along with all the Dark Aeons) is Dark Matter, so you can save up 99 for Ribbon while armor hunting simultaneously. Also note that you do not have to save and then reset to keep fighting Yojimbo. Simply kill him 4 times, board the airship, then return to the Sunken Cave to fight him again.

If you want to have a much easier time with the last 4 Dark Aeons then your only option, really, is to level up. The first 4 can be beaten with stats under 100 with a good strategy and Anima. On my last playthrough my strongest character was Yuna and her highest stat was Magic at 90. I beat the first 4 Dark Aeons without much trouble (though Dark Shiva takes a bit of luck), but you will have a much easier time if you level up and with the Don Tonberry trick it doesn't take all that long (around 30 seconds for 99 S. Levels if you do it right).

Quote Originally Posted by d£v!l'$ ph0£n!x
if u can kill dark shiva then u can kill dark yojimbo.
Definately not true. The only thing that makes Dark Shiva difficult is her speed. Dark Yojimbo, like Dark Valefor, can use an attack-all move on any given turn making him much more difficult.