I had pondered the same thing before. I can't help you with where to buy a smaller LCD, but remember that you can purchase a slightly larger screen if its cheaper to do so and not use some of it. Just install it into the mac behind the bezel and adjust the screen proportions to fit the 9" viewable area of the SE. I seriously hope you go through with an SE mod. It not often you see someone do a mod like that!
Not sure if i can afford it yet, but I'd love to, and I think I might plan for it. I looked on ebay for lcd displays and found some good ones for a decent price. search for "vga lcd", throw in a dimension like 8" if you want, they have quite a few. I'll post a mod guide if I ever get around to it.