I also use SU whisper white all of the time with my gamsol magic ...if you can really call it magic!!!
I've people in the US use Georgia Pacific with similiar success - which apparently is available in US Walmart's.
It REALLY does make a huge difference what paper you use, as SU WW has a bit of a coating that allows the pigment from the pencils to blend and * slide * a little on the paper. The other important factor is having decent stumps - the made in Taiwan or Creative Mark are so much better than the harder stumps - made in Japan.
The made in Taiwan stumps can be found via Whipper Snapper stamps - and the Creative Mark I have obtained through a volume purchase made by another SCSer who ocassionaly has stump shares .
Don't give up to easily - it took me a bit to get onto it, but now it's my favorite method of colouring ( of course, I can't afford Copics - so I don't know about them! )
Good luck!