Horizon Herbs is a great vendor. I've always been happy with the seeds and plants I've gotten from them. They are great lovers of plants - they are plant people. Plants/seeds from such folks always seem to do better for me. :) But since it is a native plant, you could search the native plant vendors for other sources of material.

I've not grown this nor do I know the germination requirements. But I've noticed that many tough to seed-start natives need winter to break seed dormancy. It may perhaps be one to try winter sowing with. I know some I have failed miserably with trying other methods respond well to winter sowing. Some of the tough ones require a semi-permanent location/bed since the germination may span over more than one year. Just some things you may wish to try or consider depending upon germination requirements.

FataMorgana