Suzi, I don’t think you can order the foot separately. That is because the bottom plate has a little plate that fits into the same space as the plastic bobbin cover and the sizes are different on 7mm machines (at least mine are different) than the 9mm bobbin covers. However, Janome might have made that adjustment with newer models than the 7mm that I own. I know that tI have 2 binder attachments that fit the 7mm & 9mm machines and a separate one for my cover hem machine too. I’m not sure what I was thinking but I did buy them at separate times and a few years apart. I really only ever use the one for my 9mm machines as I probably wouldn’t finish a quilt on my little 4120 because of the bulk that a quilt has.
Also they are quite expensive, just so that you are aware of that part of the equation. I do not regret any of the purchases that I’ve made for this attachment as it is pleasure to use once you’ve got through the practice stage and it didn’t take me long. I always watch the video every time I use it as it could possibly save me grief JUST IN CASE I forgot how it worked and so far I haven't.
