Another option, if you can't find a book, is to do fabric squares and turn them into a blanket.
We did this when my oldest went to Disneyland with my parents. We found a backing fabric (Cars - her choice) and then coordinating fabrics. I cut out the squares in 12x12 and then got a few pieces of foam board. I should have cut it smaller than 12x12 - next time I'll do 10x10 or so to allow for a border.
I sent her with fabric squares and a few different colored markers. I also sent clips so the fabric could be placed on the foam board to provide a writing surface. My parents helped to swap out fabric squares. They put the whole thing in their backpack and carried it around the park. It wasn't terribly heavy.
She got the characters to sign the squares. When she got home, we bought a few embellishment patches for certain characters and made a quilt of all of the signatures. She LOVES the blanket!! it's something she can see/use more often than a book. She's taken it to school for show and tell before.
I did not find the books here either. So I waited until we got to Disney. When I filled out the information for our hotel when booking our trip (we got the hotel/park/food package), I mentioned this was our kids first trip. As soon as we got the hotel (All Star Sports), the desk manager came up to my kids, greeted them by name and handed them free autograph books (just the 50 pages one that did not have the photo slots), coloring books and a small Donald Duck stuffed animal. I was shocked. I had not expected this. Along with a free balloon and balloon animal every day too!
I bought a package of the Sharpie Retractable Permanent Marker Pens in assorted colors (I think about $10-$12) and these were perfect. Big enough for the characters to write in and did not bleed on to the pages. We had the characters sign the right side of each page then put the pictures on the left side. My kids got completely in to this (ages 5 and 6 boys) and we got about 30 signatures on our fist visit (the guide that you pick up when you walk in to the park tells you exactly where to find the characters).
The parks do also sell the books I think for $9.95.