YouTube - Zodiac Spear from the Henne Mines - Guaranteed
Apparently, someone has found an extremely efficient (well, more efficient than the usual absurd way of obtaining it in the Henne Mines) method of obtaining the Zodiac Spear that doesn't involve missing chests that you had no idea you weren't supposed to open or taking a 1/1000 chance in the mines to look for a chest that, odds are, wasn't there.
The video in the link shows how one can almost guarantee obtaining a Zodiac Spear in the Henne Mines by taking advantage of the RNG (random number generator) inside the PS2. More details are in the vid description. Quite interesting. I'm gonna try it.
P.S. I'm so glad I was too lazy to get rid of my PS2 after I got my PS3, because for some reason, this trick doesn't work on the PS3.
Edit: Yes it does, though less is known about it, so I still recommend this be done on a PS2.