I haven't tried Whisper White and will have to order some. I got my pencils,
gamsol and blending stumps at
www.Inky Antics.com I have also seen the pencils at Hobby Lobby. Gamso is an ordorless mineral spirits. Gamso is Manufactured by Gamblin Artists Color Co. which may be why you can't find "Gamso" I don't know about a paint thinner.
You will also need "blending stumps" (cost $1.67 for 6) or tortillons as they are called at Hobby Lobby. They are rolled paper, pointed at one end for detailed blendng. Now this sounds crazy but the ones from TIAWAN are alot better than the ones from CHINA. I have tried them both. Hobby Lobby has them from Tiawan and Michaels has them from China. The ones from Tiawan blend alot better and last longer. Also in case you don't know - you can use an embry board to sharpen the tip thus removing the chalk that builds up. As the chalk builds up it doesn't blend as well.
As you can see I have done my homework on this technique and Love it.
I have SU pencils, watercolor crayons, markers etc and to me nothing makes your artwork compare to using this technique. And of course the paper makes
all the difference in the world as you have found out.
I hope this is helpful and I hope if others have found other ways to help in
this technique they will share - which of course they will! This is SCS everyone is great. :-D