The double-flowered form of Trillium grandiflorum is one of the plants that you have to earn- it is so hard to find. It is not for the unworthy.  It is not by Louis Vuitton . You won’t see one on the subway or at Walmart . It is something to dream about !
  Even ‘regular’ trilliums are seldom for sale in garden centres or through mail order nurseries. The double-flowered forms (there might be two) are all divisions of the one (or two) original oddball mutants found in  the wild !!  They produce no seed, so have only ever been propagated by division ! This woodland treasure has sold (before my own eyes, but not at my nursery) for $500.00 a pot !  We  have a few plants in stock, ready to bloom (it is  now early April) for the lowest price I have ever seen them at – $49.99 each. Google them and see what I mean !
          Should you acquire one, plant it  in brighter light than you might think it would like. An overhead canopy of deciduous trees is ideal, as this is where trilliums evolved. The summer months are hot and dry and trilliums naturally go dormant by then. Mark your treasure with a stick so you know where your trillium is planted !!!