anybody know where I could buy Claytonia virginica?

It is listed at http://www.nature-by-design.com/plantlist2007.html
Don't know if they do mail-order (either in general, or for this
plant), but you could ask them, or look at native plant nurseries near
you.

Seeing it one place is a good sign - it means that other native plant
nurseries might have it too.

This species is native to the United States (roughly) east of the
Rockies - in other parts of the country (or to a smaller extent,
world) you may have a different native Claytonia - see maps at
http://plants.usda.gov/java/profile?symbol=CLAYT