The blades are actually for a carpet rotary cutter. Here is a link to them.
http://www.harborfreight.com/catalog...ory=&q=carpet+
The actual carpet cutter is in the middle of the page in yellow. The blades will fit a regular 45 mm rotary cutter.
There is also this post as the blades from Harbor Freight are hard to come by:
http://www.quiltingboard.com/t-68213-1.htm