I'm not sure how helpful this is, but I think you're looking for Asclepias syriaca.

http://en.wikipedia.org/wiki/Asclepias

Here is a link that might be useful: Asclepius wikipedia

I have a BUNCH of Milkweed (A. Incarnata "Soulmate" aka swamp milkweed) seedlings, if you are interested.
No clue where you can get common milkweed from, but I had success in Texas, my home state with this as a monarch host plant. Up here in the Puget Sound (military transfer), I have never seen a Monarch, but it is my hope that if I plant enough of these, and share enough of them, Monarchs will eventually visit.
If you would rather wait, within the next few weeks, my milkweed should bloom and seed, and I can send you seeds then. You should be able to sow them this summer and have them start sprouting, and by next spring, they just may be large enough to flower.
Mine was a transfer seedling when I brought it up here, about 3 inches long. Second season growing and I had flowers.
A word of warning, this thing seeds like crazy!

You live in Eugene, the only milkweed you should be growing is asclepias speciosa. I'm in Beaverton and i have lots of seeds if you are still interested. email me and I can send you free seeds if you snail mail me a self-addressed envelope.

FYI, I've got A. syriaca in my garden near Seattle. It does OK, but would prefer more heat. No Monarch butterflies here, alas. A. speciosa is much prettier, shorter, with bigger flowers. A. incarnate does well here. And A. tuberosa if you can find a hot gravelly south facing slope on which to grow it.
Best,
Jim