Hi Al,
Benefit the Hips and Knees is a modification of Xiao Chai Hu Tang. The main difference is the addition of Qin Jiao (Gentian Root). I'm not sure about the back order. As far as a substitute goes, you could either order Natural Path's Xiao Chai Hu Tang and add your own Qin Jiao (I'm not sure of the ratios Kan herbs uses but probably 10 grams or so to 100g of the base formula would do it). Otherwise, Kan Herbs' version of Xiao Chai Hu Tang is called Harmonize the Qi. If they have that, you could substitute with it.
Hope your keeping warm up there in TC!
Erin