Hi Doug,
I can confirm that La Chouette (Paris) has a 52 in green right now. At least their website says so, and they are usually pretty good about keeping their stock up to date.
Of course, it's more expensive than buying direct from Riv and then there's the whole issue of moving it from France to wherever you are located.
I am located in France, I work about 10 minutes from La Chouette, I confirm that they are great and super helpful guys, and I'm happy to broker on your behalf if you don't find an easier solution (i.e. a used 52 somewhere in the US).
cheers,
John