You can sometimes find these in your local stores, but there selection can be painfully limited. And quite expensive due to the Disney licensing. Shopping for clearance if you have the time is the only way to make this worthwhile.
But if you are looking for unique, cost-effective products there are some great online resources including Etsy stores. Look at some of the stuff I was able to find for my upcoming Disney scrapbook:
DesignUrMemories offers digital papers, 12x12 papers, stickers, embellishments and more in their Etsy store. I got some amazing Disney items, but she also offers all sorts of scrapbooking supplies in various themes.
This layout was done by ImAsMADaSaHaTTeR - so fun! She does all kinds of Disney things including scrapbook layouts. Buying pre-made layouts can save you a tone of time and money. However, you can also occasionally pick up individual scrapbook supplies in her craft section if you prefer the creative process to simple, quick and easy.
OhioScrapper has a variety of page layouts that include incredible paper pieced items like this Mickey, "Mickey Mouse" wording and these stars. I was pleasantly surprised when these arrived as the paper piecing give the page amazing depth and a more polished look than many layouts.
Single page layouts are $15 and two-page spreads are $24. She does much more than just Disney and they're all gorgeous and made with the same attention to detail.
This is a different kind of page layout - it's a kind of overlay that you can put paper and pictures behind to create a unique scrapbook page. OldPineShop offers an array of these. You can actually request the color you would like it on. One of them has the Disney castle image . . . it would look incredible in front of so many Disney papers! These cost about $6 each.
I received a couple of paper piecings like this from PapercraftCollective. From what I can tell, they don't usually just sell the paper piecings, they seem to do cards starting at $4 and layouts only at a cost of $7 for individual pages and $14 for 2-page layouts.