I do have some nice doubles (ordered a few more for this year). Always double... Big Kiss, Dorothy and Toto, Double Intrigue, Kwanso, I Suppose, Infinity, Merry Morgan ... while Merry Morgan is not reliably polymerous, has been reliably double. Peggy Jeffcoat (on order for this spring) - in the display garden - showed nothing but double blooms... would ask some of you who have grown her longer - does she ever not have doubles?
More "always double" - Silent Thunder, Siloam Double Classic, Spotted Fever, Unlock the Stars and Yellow Bouquet (which also produces polys every year).
I don't have any 'doubles' that have never doubled, though I do have a few that throw single blooms... Dewy Sweet, Exotic Etching (listed as double 90% should be listed more like, double 40% ... maybe), Flamenco Christmas, Night Embers, Schnickel Fritz ---
absolutely love
this one... it not only is 'nearly always' double, it also produces polys ... including a single-form poly. Not 100% double, but absolutely gorgeous.
Lastly, Flore Pleno is triple... but once in a while, will have a double among the rest of the blooms.