The white form should be well established in cultivation now as I introduced a quantity of seed about 10 years ago. At the time it was on the "pink" sheet of the NCCPG (now Plant Heritage) as either endangered or lost to cultivation though I believe there were always a few in some collections, e.g. Harry Hay's. It does hybridise freely with the dark form and probably would need keeping seperate if you want to produce your own seed.