The Grange in Issaquah sells Bio-Diesel. Not sure what flavors. 5%, 10% 30% etc. I've thought of running in my 06 F350 but you have to read the warrenty info. Ford stats anything over 10% bio will void it. I think the big concern with bio is it has a tendency to detiorate rubber hoses etc. Now is this true or not, I don't know. I've also read of people having to replace their injectors since bio-diesel doesn't compress the same as #1 or #2 Diesel.
Here's a good site for information:
http://www.biodiesel.org/buyingbiodiesel/retailfuelingsites/
Edit:
The Grange is located just off Front street and is directly across the street from I-90 Motorsports.