You might try Heronswood Nursery (link below).
I have purchased large, blooming sized Hellebores from them during the past several years and have always been very satisfied with quality and service.
I would contact them, to determine if they ship them during this time of the year or wait until fall.
Most other vendors that I'm aware of, sell only small pots by mail-order and any larger sizes are only available during on-site sales.

Here is a link that might be useful: Heronswood Hellebores

Thanks for the suggestion, ladywindsurfer. I kept searching after my post and found a place-- Pine Knot Farms. They have great reviews at Dave's Garden. I emailed one of the owners, Judith, and she said that some of their 3 quart and larger plants are blooming size. I will probably place an order soon!

Here is a link that might be useful: Pine Knot Farms

Have never purchased any Helleborus from PKF. None of their listings were that impressive to me.
As a collector, for about 25 years, I am only interested in very unique colors and color combinations. Yellows, slate, blues and near black are my current interest.

I have received numerous hellebores in all of the above colors and more from PKF, and some have actually been shipped while in bloom. As you probably are aware, other than tissue cultured plants, which at this point usually will not be available in blooming sizes, it's pretty much a necessity to choose plants while they're in bloom if you want very specific colors, patterns, etc. The Tylers at Pine Knot have selected plants for me in the past based on pics I've sent them, etc., but that, of course, has to be done during the bloom season.

Its nice to hear from someone else that has ordered from PKF. Judith was clear about which plants and sizes she could guarantee colors. I ordered a 6 quart "Pine Knot Select Darkest" and one 3 quart each of "Red Lady" and "Blue Lady". They should arrive next week!

I've heard good about both Heronswood and Pine Knot, and I'm sure you'd be happy with either. I'm certianly pleased with the plants I purchased from each. I have also grown many plants from Pine Knott seed, and it's fun but does require patience. Out of a batch of 50 seeds I have the usual whites and pinks, but also yellow, red, almost black, purple,double, anemone, picotee, spotted and veined and solid colored.... I was amazed at the variety and the quality.