This link might be helpful. I haven't checked out the sites but they might be of interest

Here is a link that might be useful: Sweet peas

They have cuthbertsons listed.

Here is a link that might be useful: Cuthbertsons

Thanks for those sources. I'll order some from one of them. Next question- when should I order seeds, and when should I plant them in coastal central California?

I live in New York City, but from what I understand sweet peas are sown in the fall for winter bloom in California; when exactly is the best time in your area I don't know. I remember reading somewhere that sweet peas will not set buds when the days are short, so you might want to take this into account. I have heard of short day sweet peas, DiGiorgi used to carry them. These are grown in greenhouses for the cut flower trade, I don't know if they do well in the garden. Good Luck.