Here are some alternative, non-commercial sources for seed for ornamental plants.
As a member of NARGS, you are eligible to participate in the annual seed exchange held in January. Members receive 25 seed packets from each year's exchange.
Members who donate seed to NARGS receive 35 seed packets from the exchange, and their seed requests are given priority over non-donors.
Seed for many of the species listed in this exchange is unavailable through commercial sources, so it's a useful source for gardeners who collect alpine plants.
GardenWeb Forums Seed Echange
GW on the net
The GardenWeb Forums are my favourite place on the net to discuss gardening, particularly the GW Perennials Forum.
There are many different forums available at GW, one of which is the Seed Exchange. This is a forum for gardeners from around the world to offer seeds for trade and make requests for seeds they are seeking.
Grasslands National Park Prairie Grow Program
For information email: Adrian_Sturch@pch.gc.ca
The Grasslands National Park is involved in revegetating several hundred acres from farmland back to grassland. They are seeking the help of gardeners in this endevor.
They will provide you with seed they have collected from wildflowers growing in the Grasslands Park. From this seed, you grow wildflowers which you get to keep in your garden. Each fall, you collect the seed from these wildflowers, and send it to the park staff who use it to revegetate grassland in the park.