Shepherd's purse aka Capsella bursa-pastoris can be purchased in seed form. Do a google with:
Shepherd's purse seed
Capsella bursa-pastoris seed
I don't know where either of you live, but it's considered a weed in many areas where it is not native. It's a warm zone plant and reseeds prolifically each year. Here's some info on it including where it is native to.
Capsella bursa-pastoris - Wikipedia, the free encyclopedia
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.