I've grown L. parvum from seed - nice little lily. I wasn't nice to it, so it hasn't flowered and I still don't know if it got lost in the move. Lilium washingtonianum - I doubt anyone has bulbs. But seed is available fairly often from various seed exchanges, not so much from commercial sources. The seeds germinate without much problem and I have a tray full right now. I have mature bulbs of what are either washingtonianum or a wash. hybrid; they haven't bloomed so I'm waiting. If you saw where they grow in the Cascades, as I have several times, you'd understand why they're a pain. Often they're growing up through other shrubs in sun on well-drained slopes...
About all I can suggest is researching their habitat and trying to duplicate it.
About all I can suggest is researching their habitat and trying to duplicate it.