dipmicro - 6,8,10 pins
http://www.dipmicro.com/store/HDR06X1FL
http://www.dipmicro.com/store/HDR08X1FL
http://www.dipmicro.com/store/HDR10X1FL
Stackable Header Kit 20x 8-pin & 20x 6-pin 0.1 (Total 10 Arduino Shields) - dipmicro electronics 20 pieces each 6 & 8 pin
I searched this weekend at mouser, I don't believe they carry them.
Digikey lists Samtec headers, but none in stock, long lead time, expensive.
Sparkfun also carries them as sets.