The three nurseries where I buy hostas are Green Hill, Naylor Creek, and Savory Gardens. Never, never buy a hosta from any of the "big box" stores. There is too much risk of getting hosta nematodes or hosta virus x. From what I understand, once you have an infection of either, forget about growing hostas. Maybe I am exaggerating, but it is a risk I don't want to take!
Savory Gardens was started by Bob Savory, noted hybridizer whose best known hosta is probably 'Golden Tiara'. I have added several hostas recently hybridized by his son, Dennis, also a very talented hybridizer.