I thought someone else might be interested in this. Amazon has the free motion foot in the link below for a very reasonable price. Even though it says it is a Singer part, I went ahead and ordered because it looked very similar to one I have on a Kenmore. And it worked out that it does fit my Kenmore 385.19233 (made by Janome). So it could possibly fit some of the Kenmore 158's out there too or other low shanks.
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
Serita