Mrs. Robb's Bonnet and other wood spurges are deer resistant because the characteristic Euphorbia milky sap is slightly poisonous. Some gardeners with sensitive skin have strong reactions to the sap.
Some references say Euphorbia amygdaloides is native of Asia and invasive. Others say it is a European native that grows slowly. Ah, the experts.
Hardy to 10 below zero F, zones 5 to 9. Great for rock gardens, pots, mass plantings in dappled shade.
There is an International Euphorbia Society. A link to their site is here. Look on the links - tips for harvesting and cultivating seeds as well as taking cuttings.
Several nurseries offer the plants, but so far, I've found only one source for seeds, a German company, Rare Plants.
I'll keep looking for seeds since I'd like to have a couple of flats of plants for the dry shade around the Osage Orange trees in the back.