Your wanted list includes:
Rhododendron arborescens.. Sweet Azalea
Rhododendron calendulaceum..Flame Azalea orange
Rhododendron canescens..Piedmont Azalea

RareFind Nursery in NJ has these at:
Arborescens
Calendulaceum
Canescens

Greer Gardens in OR has R. arborescens at:
Arborescens

They are run by Hank Schannen and Harold Greer respectively. These two men among the leading rhododendron experts in the world. They are both active members in the American Rhododendron Society and extremely well known among people involved with any aspect of Rhododendrons.

Here is a link that might be useful: Calendulaceum are Rare Find Nursery