here is a link to a reputable dealer in blades. Please read his ad.
http://www.houseofhanson.com/lpsharp.html
Remember, your old blades should never go into the land fill, so save them in a safe place, send them in for credit on new ones. Get them for $3 each if you are using 45 mm blades.
I recently got 10 blades (new Olfa in their original package) for $30. No added postage. This is the best buy I have found.
June in Cincinnai