Yikes! You can check your local Home Depot or Lowe's, but it's not a for sure thing they'll be there. Your best bet would be to see if you have a local tack store (horses, etc). If you had more time I would suggest <a href="http://www.slingrings.com" target="_blank">www.slingrings.com</a> Hope you can find what you need!
I used macrame rings for the first one I ever made. They are brass rings found in the craft section of, shhhh walmart, or other craft stores might carry them but I know wm does for sure. Not ideal but in a pinch definitely work. I used that sling for over a year, and with a heavy child. <img alt="" class="inlineimg" src="http://www.mothering.com/discussions/images/smilies/smile.gif" style="border:0px solid;" title="smile">
I've gotten some from Sling rings several times now. <img alt="" class="inlineimg" src="http://www.mothering.com/discussions/images/smilies/thumb.gif" style="border:0px solid;" title="thumbs up"> Highly recomended!