If memory serves, Break HP Limit is made by using 30 Wings to discovery on a piece of armour. Wings to Discovery can be found:

30 - In the calm lands-remiem temple. Win the chocobo race and finish with three open treasure chests and no bar-thingys.

4 - Bribe Malboro for 135,000gil or more.

1 - After beating Shinryu in Monster Arena.