The breeder, Mrs J Abel Smith was from Hertford, England. She passed in 1995. Many of her creations were sold through the Orchard House, also in Hertford, England.
Sometimes foreign bred daffodils are only available in the country they were bred in unless picked up by a major retailer and purposefully grown under contract
Orchard House did ship internationally. I don't know if that place still exits as the listing that I saw in Daff Library carrying her daffodils was from the 1970's.
I'd say your best chances of finding that daffodil would be an English source.
