Iji sells Somber stones. The Claymore can't use 'em - but the big sword you got with the Weeping Penninsula Boss does. A +4 Grafted greatsword used two-handed is about the same as a Claymore +12 at a rough guess. Hitting L2 gives you +5 on every stat for a couple of minutes.
But you only need 1 each of +1 to +4 for an upgrade on Somber weapons.
But you only need 1 each of +1 to +4 for an upgrade on Somber weapons.