They don't seem to have made it to any of the common distributors that I've checked. My guess is that they haven't gotten the quantities yet where they can do that. The HiFive1 is only a few months out on the market and the only thing using the chip they had made. It seems to have done well (~1k of them sold in the crowdfunding it looked like). So I hope we'll see them start to show up soon, even if you can't get them in massive quantities yet.

More like one week on the market. The first boards shipped the 23rd of December.