i've been getting all these really neat items which I can use to customize stuff, but I can't get enough to actually accomplish the customization. for example, I won Dark Matter for winning 1st place in a blitzball league season, but I can't seem to find any more anyplace.

so my question is this, is there any easy means to duplicate items like this? more mega-elixers would be nice too since i only found like 4 before fighting Omega weapon.