How much do you need? I might be able to help - I use it for weighting down the hems of bata de cola skirts - I'll go see if I've got any left.
ETA: Sorry, my mistake - I've got 1/2 centimetre not 1/2" But have you considered trying your local friendly DIY merchant? That's where I get a lot of my cord from and it's where I got my last lot of bag piping cord from - polyethylene rope comes in all seizes and colours!