I am using Bergeon Rodico clay, made in Canada.
I also use green Rodico clay, which is Bergeon.
I don't like either one. They dry up and if you try to stick a balance wheel in them to check it out or hold it, you'll bend the wheel.
I had some that was gray and can still use it after 3 years. I just can't remember who makes the gray clay.

Patrick,

I keep my Rodico in the plastic bag it came in and have that stored in an air tight plastic (pill) container. I have been using the same piece for over three years now and it is as fresh and flexible as the day I opened the bag. Hope this helps.