Local chapters of the Washington Native Plant Society have great plant sales. The Salal Chapter of the Washington Native Plant Society has spring and fall sales at their Native Plant Demonstration Garden on Memorial Highway in Mt. Vernon. Order early for best selection! Email nativegarden@fidalgo.net to sign up for their mailing list.
The Snohomish Conservation District has a huge native plant sale early in the year (usually January). Their plant sale page has links to other conservation district plant sales and nurseries that offer native plants throughout the year. Conservation district plant sales offer bare root plants at low prices. Be sure to get on their mailings lists early so you will be notified about sale events.
Local nurseries carry a variety of native plants and many are increasing their inventory of native plants, including Orchard's Nursery in Stanwood. Let them and other nurseries in the area know of your interest in purchasing plants that benefit wildlife and thank them for their support.