Please tell me that you haven't used that trapezohedron you got yet...
I used it after I bought a Dragoon Lance and upgraded it, to have the highest STR weapon possible for Fang. Why?
Oh, you used it on a dragoon's lance. Then my point is still valid then.
If people are short on trazohedrons you only need one and ypu can turn it into three of them. make either Kain's Lance (made from Dragoon Lance, Shamanic Spear, Punisher, Pandoran Spear or Gae Bolg) or Nirvana (made from Tigerclaw, Healer's Staff, Belladonna Wand or Mistilteinn).
Get one of the weapons to * in the rnk after you upgraded them from the base weapon listed and then dismantle it you then get 3 trapezohedrons and 36 moonblossom seeds (sells for 216, 000 gil)