Hardanger is normally worked in two weights of threads. For fabric with count of 22 through 25 I use size 8 and size 5 threads. Kloster blocks are worked in the heavier, thicker size thread which would be the size 5. Bar weaving, and fill-in stitches are worked in the lighter size 8 thread.
For further discussions of threads view my blog page: Needles and Threads
If ordering online I have found it is a good idea to always check the S&H costs and shipping time before clicking that submit order button.
Near all of these below stores carry threads and most offer cut-to-size and pre-cut size fabric pieces. The below photo shows a small slice of Needleworkersdelight order page where you specific pre-cut size and fabric color choice.
URLS for thread, fabric, stretcher bars and other supplies:
needleworkersdelight.com (custom dyed fabric) (USA)
http://www.needlestack.com/ (needle in a haystack) (USA)