Do you know of any plant and seed-sharing sites where I might find some peonies, for example? Or where I might post some stuff I have no place for?
Most reliable seed exchange programs require membership, but . . .
PEONIES:
If you are interested specifically in peony seeds, the American Peony Society and the Canadian Peony Society are excellent sources.
You might also consider contacting the Pacific Northwest Peony Society. They are fairly new (est. 1996) and might not have a seed exchange yet, but can be helpful with other information.
DONATING PLANTS:
There are several places locally that list plants for donation.
Plant Amnesty has an Adopt-a-Plant program.
Also, try the Pacific Northwest Garden Exchange at Houzz.
SEED LIBRARIES:
This is a relatively recent phenomenon and many cities now have such programs. Here are some examples:
King County Seed Lending Library
Northeast Seattle Seed Library
SOCIAL MEDIA:
There are groups on Facebook devoted to plant and seed exchanges. Be aware that not all of them are cautious about excluding aggressive or invasive species.