A search came up with several mentions. According to this Gardens Illustrated link (scroll down), it is not yet available by seed.

ETA: https://www.gardensillustrated.com/plants/summer/hollyhocks-how-to-grow-alcea

I couldn't see a link and a search only resulted in a named variety of alyogyne (whilst in the malva family, not an alcea)

The relevant section in GG's link:

Alcea ‘Sheppard’s Delight’

Not available to buy just yet but hopefully will be in the years to come. The unusual salmon-pink semi-double blooms are from a self-seeded plant in Jonathan’s garden, and he’s now working to isolate the flowers and save seed. 2m x 1m.

O, Cheers. Need to pay more attention to spelling (and tendency to charge onwards with an attention span of a mayfly)