I thought I'd pass along a few tips I've discovered in trying to find sewing supplies in bulk for a decent price.
The first place I started was Ebay. You can find just about anything and most of it is very affordable if ordered in bulk. A lot of places in Asia will ship for free too!! Awesomeness. :)
Here's a link to the sewing supplies section of Ebay:
Now that I'm on Etsy, I've discovered that you can get all kinds of supplies there too which is great b/c they're sold by crafters to crafters so you can get a lot of neat things for decent prices as well.
Here's a link for these as well:
I've also found it useful to look on Kijiji sometimes. Occasionally people will be looking to clear out their craft rooms and will practically give things away for free.
I hope this has been helpful. I live in a small city and was having a really hard time finding what I needed. The added bonus to Etsy and Ebay is that they are delivered right to your door!! I love it.