It all depends what that seed is for. If this is a Transportation Crystal seed (Tiny Elf Crystal), then dropping it permanently loses it. Slaying Elves will get you another. If this is a Crystal Bow or Shield seed (Crystal Seed), then dropping it permanently loses it. Buy yourself a new bow from Islwyn for 900k or a new shield for 750k. If this is a Crystal Saw seed, (Small Crystal Seed), then I would first try going back to King Narnode Shareen for a replacement. Then Brimstail in his cave, then finally Hazelmere on the Spider Island. I haven't had that bad luck myself, but the guides are silent on the matter of Crystal Saw replacement.