Normally we strive to sell only pure elements but we make exceptions where it concerns radioactive ones. And in the case of thorium at least it has much more to do with practical reasons than with safety. While radioactive, thorium's atoms are relatively stable and thus decay very slowly. Want to wait around for a piece of thorium to whittle away to half its size because of radioactivity? That would be a 14,000,000,000 year long wait. By then the solar system will be long gone.

Anyway, we said practical reasons are what motivated us to get impure thorium. As in it's otherwise practically impossible to get the pure metal. The alternative is thorium dioxide, a white powder, which is still plenty expensive and hard to get at $50 a gram. Ouch!