There is a shop in North Seattle, www.kicks-hobby.com, that sells the .S sets. I've purchased the Mario, Luigi and Link sets, plus they have Pac Man, Dig Dug, Donkey Kong, Balloon Fight, and Ice Climber.
The Bubble Bobble one is hot sex, I need that now.
There's a similar thing in Germany, called "Ministeck" (www.ministeck.com) from the seventies, I believe (I had some of these when I was little in the 80s). There are different shapes of the Blocks and they are pretty small (1 "pixel" is 3 millimeters). There are 23 basic colors.
I bought a pack of these from EBay and a reseller (www.pumiko.de) and started to make custom motives: