http://www.collectorsnursery.com/html/perennials_p-s.html
Try "petasites" with an S, and you will see several nurseries. It sounds a bit aggresssive.

You do not want to plant a Petasites Japonicus if you love your other plants. The Petasites Japonicus will consume and take over the garden and will invade your landscape and that of your neighbors by underground runners. I have been trying to find a way to get rid of it and have not been successful other than digging it up every time it shows up in the garden which is daily. Beware of this beautiful plant. Don't let it's beauty entice you to plant it.

Since you are in Sacramento, petasites will take over your yard. If anyone lives close to Eugene OR, please come and dig rhizomes from my yard! LOL I actually resorted to Roundup blackberry spray, I carefully used only a drop on each leaf, and it worked, altho it is still appearing in other far-reaching parts of my yard. I wish now that I had planted it in a container, because it is a wonderful large tropical-looking plant. Since it is eaten in Japan, I wish I knew how to prepare it. I could feed my whole neighborhood.