i bought mine on ebay for a reasonable price. i bought several because i havent found a way to sharpen them yet either.
there are some good prices on ebay for rotary blades. here are some for pinking:
http://www.ebay.com/itm/OLFA-45mm-RO...item35b5924e56
http://www.ebay.com/itm/OLFA-45mm-PI...item519b0750f6