Several commercial growers carry at least some of the gesneriads you're looking for--check out Lyndon Lyon Greenhouses, Lauray of Salisbury, Kartuz Greenhouses, and Violet Barn.

But your absolutely best source is the plant sales at a local chapter of the Gesneriad Society--they will often have plants that are new, rare, or otherwise unusual and not obtainable anywhere else. Check the Gesneriad Society website for contact & meeting information for the chapters, as well as a list of commercial growers.

Here is a link that might be useful: Gesneriad Society

Yucca Do Nursery in Texas has a number of hardy sinningias, including at least one you list (and a lot of others.) I've got most of them, and am very pleased. I hope you have a gesneriad society near you, tho'--as John says that's a great way to get them. If you don't, try to get to a convention! Great people, lots of interesting information, and plants grown the way you've never seen them.