My 2 favorite rhododendron nurseries are:

http://www.rarefindnursery.com
Rarefind Nursery with Hank Schannen in Jackson, New Jersey
Enter "Dexter" in the search field and you get 16 varieties.

http://www.greergardens.com
Greer Gardens Harold Greer in Eugene, Oregon
I found 5 Dexters.

At least 125 of Charles Dexter's 145 known hybrids are raised at Heritage Plantation in Sandwich, MA.

Some of the best known are:

Apritan - Fragrant apricot blush with large flowers, also known as Dexter's Honeydew

Bell Ringer - Creamy white Dexter derivative from Tony Consolini, very rugged with dark green foliage. One of the best doers.

Betty Hume - Huge pale pink

Brown Eyes - A classic, with large pink trusses set off by a strong bronze flare in the flower. It is very hardy.

Consolini's Windmill - A stunning picotee-type flower. Does best in a site with dappled shade.

Dexter's Apricot - A compact plant. Flowers with darker edges and yellowish-green basal blotch.

Dexter's Giant Red - Bright red, fades to dark pink with a red blotch and red spotting. The truss is huge.

Dexter's Orange - Darker pink with an orange blotch that gives the truss an overall orange glow.

Dexter's Purple - Rich lilac/violet with a deeper flare in it's throat.

Dexter's Spice - Huge fragrant white

GiGi - A favorite Rose Red with "freckles"

Great Eastern - Similar to Scintillation, but slightly later and can take full sun.

Heritage Best Orange Salmon - Pastel peach-colored trusses cover the plant.

Janet Blair - A Dexter derivative from Dr. David Leach

Merley Cream - Creamy white with a prominent yellow green blotch.

Parker's Pink - Bicolor pink with bronze throat. Excellent!

Rona Pink - Fragrant silvery pink pinnacle.

Scintillation - The most widely grown Dexter in the Middle Atlantic region but gets burned leaves in full sun.

Todmorden - Bicolor with rose edge and white center. Seems to need sun to bud up well.

Tom Everett - A superb lavender pink

Wheatley - A Second Generation Dexter by Howard Phipps, A favorite pink!

Thank you very much, rhodyman!!

PlantMarker

Please be careful buying Rhodos from the west coast and planting on the east coast. You may encounter some problems when planting at certain times of the year.

The best East coast nurseries that I am familiar with are:
Rarefind, and Eastern Plant Specialties. Eastern has some very large Dexters for sale from their location in Maine.

Rhodyman,

I have Wheatley, Brown Eyes, Scint.
My favorite is Wheatley.
I also have Pinnacle, but am not sure if that's a Dexter.
Perhaps you would know?

Pinnacle is a catawbiense hybrid by Tony Shammarello. It was introduced in 1955. It is a very tough plant having bloomed after a -28F winter. It is the proud parent of:

Big Boy: Pinnacle x Brown Eyes by Robert Blough
Pink Hydrangea: Pinnacle x Pinnacle by Robert Blough
Robert Hinerman: Pinnacle x Goldsworth Orange by Dr. Doren Hinerman
Sham's Candy: Pinnacle x Pink Cameo by Tony Shammarello

Wheatley is not a Dexter. It is Howard Phipps cross of Westbury x Meadowbrook. This is the same cross that Phipps used to produce Brookville. Westbury is a Dexter but Meadowbrook is a Paul Vossberg cross. Wheatley is often grouped with Dexters and Dick Murcott thought that it was actually an open-pollinated Westbury seedling and not the cross with Meadowbrook that Vossberg wanted.

Here is a link that might be useful: Dick Murcott's website

Rare Find cannot ship Dexter's Honeydew to CA, and none of the nurseries on the West Coast that I have contacted breed that much revered fragrant variety. Does anyone know where you can actually purchase it mail order?