In a way you've answered your own question. You need to open four chests and not hit any poles to get the 30 Pendulums.

Alternate ways of getting them include:
- Defeating Neslug in the Monster Area (common drop, x1 (normal), x2 (Overkill))
- Bribing a Master Tonberry in the Omega Ruins (x3, 960,000 gil)
- Bribing Ultima Weapon in the Omega Ruins (x99, 1,400,000 gil)