I'm assuming that you don't know the exact name/location of this seller?

I suggest you call the FDA with what you know -

The FDA asks that anyone who has knowledge of sales or distribution of turtles less than 4 inches in length to report the location and circumstances of the sales directly to the FDA office nearest their residence.
http://www.fda.gov/AboutFDA/ContactFDA/default.htm

Good luck. Poor turtles.