I get mine from local stores like Sam's and Costco. I also found an awesome writing pad set from Mead (you can get it at Walmart but I bet you can buy it online at Amazon or the Mead website). There are different levels. One has the top and bottom line raised so the child actually feels where to start and stop. That really helps younger kids. There are levels for older children as well.
Last year, I had half of a ream printed (from a website I found through this group) at the blueprint shop where I get everything printed or bound. A professor friend offered to photoshop some in the format I want, with little pics or background themes for unit studies or whatever, but LO isn't writing yet so I haven't taken advantage of the offer. I had never even considered that possibility, and I can't wait to buy photoshop one day to play with it for homeschool. (I feel like I'm saving for 9,000 different wish list items at any given moment.)