Some place along the line I did find a three slot armor for Wakka with Break HP Limit. I can't remember where anymore though. It is best to find a four slotted armor with nothing already on it and add it by collecting 30 Wings to Discovery. You can win these by killing the Shiyru at the arena. He is hard and you need to be fairly beefed up to beat him. If you overkill him, you will get 2 Wings to Disc. So 15 x 7 = 105 times you have to kill him. You can also bribe some from the Malboro. You can get 7 to 8 of them for 2,000,000Gil.
I know this is time consuming but I haven't found a better way. By the way though, Adamantoise gives out a lot of 4 slot armor. If you collect a lot of it and put Sos Regen on it (12 Healing Springs) it becomes worth 75,000Gil and you get 40 Healing Springs by defeating the Kottos. Varuna gives a lot of 4 slot weapons but I haven't found an easy way to make a lot of money off of them. Besides the Adamantoise drops 4 power spheres and sometimes 8. If you use distillers you can get a lot of spheres very quickly if you need them.
