If you have one of the items from the book, try it. I'm going to assume that this is a bug since I and many others have tried a couple from the book that did not work. The curator does not take all the items in the book like she says. If you still need another item, there's a book at the back of the museum that lists all of the artifacts that the Museum takes. If you have an item in your inventory that works, the item's name should appear as a subject in the conversation window, so simply talk about it and then donate the item for your second piece. If you still carry the Dagger of Symmachus that Helseth gave you, now would be a good time to talk to Torasa Aram and 'donate the item' once you tell her about it. If you ask her about it, you'll need to donate a few items to the museum before she hands over the piece. Speak to the curator, Torasa Aram, who believes she has a piece around the same era, but that she won't give it to you without proper compensation.

One other place deals in antiquities and rare artifacts. Once you've done this, talk to Karrod again about the pieces of the blade and he'll now give the piece to you. If he does not talk to you about the subject, go over to King Helseth, and receive your next non-official quest, which is to find out information about Almalexia and her plans.

Go to Karrod and ask him about the 'pieces of the blade', and he'll give you his piece willingly. Find her in her chambers, and talk to her about the 'pieces of the blade', and she'll say that Helseth's (former) champion, Karrod, has a interesting piece that matches your description. It's best to start with artisans who deal in unique items, or perhaps from an enlightened person who's possibly already been of help to you. Once you have them, you're to find a 'craftsman' who is able to 'forge the blade'. She gives you one piece, and your job is to find the two remaining pieces of the broken blade. Speaking to Almalexia again enlightens you to a few things about your past life, and she'll tell you about the blade that you once owned in another life, Trueflame, who's pieces were once lost, but are believed to be in Mournhold.

Masque of clavicus vile morrowind