You can find them on amazon.com, Linens N Things, Bed Bath and Beyond, and even at your WW center. They usually run $20-60, with the non-digital versions costing at the lower end and the high-end digitals at the top end. I think mine cost $30 and is an old WW digital scale (not the new one they have now with all the points values loaded in).
If you have a kitchen store near you, that's where I got mine. It's a tiny little thing for traveling, so it packs up nice and small. I paid $11 for it and it seems quite accurate. It's probably not as reliable as some of the more expensive ones, but it works for me!
I have the new WW one with all the points loaded into it. I love it. I use it everyday. You can type in the food and then weigh it and see exactly how many points it is. Or you can use it just like a regular scale. I think it was $30-35 when I got it. Definately worth it!
I have two, one for larger items, and one for parts of ounces, I've had them for a long time. I should get rid of the two of them and just get one digital. My mom got my dad a digital postal scale for Christmas, he really likes it. I'll have to ask her where she got it.
I like the idea of the being able to get pts. right away with the WW one. hmmmm....