Here are some hosta dealers I have had good luck with.
In The Country Gardens and Gifts. Independence, Iowa
Dawn's Bloomers Independence, Iowa
Flying Frog Farm Indianola, Iowa
Dry Creek Hostas Marion, Iowa
The Hosta Leaf Colesburg, Iowa
Green Hill Farm Chapel Hill North Carolina
Naylor Creek Nursery Chimacum Washington
All of these dealers sell very nice hostas at a very reasonable price. With the exception of Hosta Leaf and Dry Creek Hostas all have websites and do will do mail order. These are by no means the only good ones around, they are just some that I have done business with.
Here is a start. Everyone else chime in with their good sources.
Gary