Phyl,
I can't tell you where to get that, (I'd like to know too) but I can tell you that the same thing happened the first time I planted a few pips given to me by a friend. It's all in the location. They like moist soil in shaded areas. I do gardening for people as well as grow cut flowers, and I have seen lily of the valley spread and take over areas. I now have the pink one too, growing in a shaded area, and it does just fine.
Cheryl

Good news Cheryl!
I FINALLY found a source....the ONLY USA source I could find.
Carroll's Gardens in Baltimore, MD. area.
$12.95 or so for 1 pip I believe, but it's a tetraploid. Says twice the height and size of regular lily of the valley. Best for cutting they say.
BTW, I am wondering, would it grow well in a planter, so that I could keep it from invading my other shade plants? (I don't have much shade in my yard). :0) Phyl

Phyl,
You could put it in a planter, and then sink the planter down in the ground, just leaving a couple inches of it above ground. That should keep it from spreading, and also keep it from drying out too much.
Thanks for the source in buying some, but I think I'll look for it a little closer to home.
Cheryl

That's a great idea Cheryl. Thanks for posting it. I wish I could find it closer to home, but doubt it. :0) Phyl

Here is a source for the lily of the valley Fortin's Giant. I recently got mine from Seneca Hill Perennials of Oswego, NY. She has on online catalog @ www.senecahillperennials.com . I hope this helps even though the original posting was so very long ago, but if you are like me, I don't ever stop looking for that 'have to have' plant.

Thanks, Margot. I don't live far from there at all. Maybe I'll take a trip up there on my school break in a week or two! Wow, were you up here visiting from CT? :0) Phyl