The answer is an awkward "yes"

They are "designed" for circulation, but only ever get sold as collectors items. Banks won't stock them but you can order rolls or bags of them from the US mint for a little over face value (I ordered a roll of the space shuttle ones to the UK)

I'm not sure what stops the USA using dollar coins in circulation, I assume there's no legal requirement for banks to stock them?

(The fact that's there's currently at least three different sizes of US dollar coin that is legal tender probably doesn't help either)