Search on ebay under the category:
craft then fabric then fabric embellishments. You should see elastic then put in the key words 2 way stretch elastic. You should find it successfully. If you see some others are selling, ask them the same question first before you bid.
Also check hancock or joann fabrics online they sell 2 way elastic.
I have made kids headbands from that so you should find it in those places.
I would check of Hobby Lobby, or even the thrift store, but that could be a bust. But any hobby shop should have what you want. Now that you bring it up I want to make one for a White Sox game, that when Halk Harrilson screams "stretch, streatch" for a home run I could have a piece of elastic, meaning much wider than your referring to but I thought it was a great idea, may even get us on tv.