Check for dealers that stock Helleborus x ericsmithii. Sunmarble is a local name given to that species by Sunshine Farms. There are also several cultivars available, including one's named: 'Pink Beauty' and 'Silver Moon'. Check with your local nurseries and box stores. Several GW members have reported finding them locally and at a lower price than mail order.
If you are primarily interested in the silver patterned foliage, might also look for Helleborus 'Ivory Prince' and some cultivars of Helleborus x sternii.
Rb

I bought one from Barry Glick, and despite his nursery's iffy rating, it thrived and is a great plant. It probably helps, though, that I bought it in person, at a plant sale -- so I was able to see that it was in great condition.

Folks in the southern New England region (including the original poster) should check out Quackin' Grass Nursery in Brooklyn, CT. Wayne has nice, healthy plants of 'Sunmarble' brought in from Glick as well as plants of Glick's first TC double x hybridus clone. Wayne also has many other hellebores and a treasure trove of additional herbaceous and woody material. Plus excellent display gardens. Worth a trip!

Here is a link that might be useful: Quackin' Grass Nursery Homepage

Sorry Barry has an iffy rating. I have found him to be helpful with questions about a diseased hellebore and a group of us went together to buy 50 hellebore seedlings which were very healthy and just as advertised.