Are there hempcrete countertops?

Yes and no!
There looks to be no reason why you or someone could not go ahead and make Hempcrete countertops. You definitely could.
Should you, though?
Remember, Hempcrete has the same properties as concrete, so you would still need to outline it and have some rebar wire in there or something just like you would if you were making concrete countertops.
Also, I don’t know how a Hempcrete countertops would react with food, so you would need to have an epoxy finish on it or something similar to keep everyone who eats off of it safely.