Here's the link to the site. It might be hard to collect 25 pairs on your own, but might be worth checking with your local coupon group to see who wants to team up. Unfortunately it doesn't say how much the coupons are worth or if they can be used in conjunction with other old navy offers.

http://terracycle.ca/en-CA/oldnavy

Flip-Flop Brigade®

Every time you send your old flip-flops to TerraCycle, you’ve done a green deed for Mother Nature by diverting waste from our landfills. To show our gratitude, for every shipment of 25 pairs of flip-flops received (about 8164 grams or 8 kg), you will receive exclusive coupons from Old Navy to distribute to the participants who helped you collect.
It’s totally free to participate in a TerraCycle Brigade. There are no signup or participation fees, and the shipping is covered by the program. Once you’ve joined the Flip-Flop Brigade, follow the steps below to earn your Old Navy coupons:

  1. Collect 25 pairs of flip-flops (all brands are accepted) and fill up a box or bag. Remember to always reuse a shipping box or bag and use eco-friendly padding as needed. To receive your Old Navy coupons, you must ship at least 8164 grams or 8 kg, or at least 25 pairs of flip-flops.
  2. Download a pre-paid shipping label from terracycle.com. Just visit your TerraCycle account online, and click “SHIP US YOUR WASTE”. You can print it out yourself or request a label from TerraCycle.
  3. Ship the box to TerraCycle by affixing the pre-paid postage label and contacting UPS to have it picked up the next business day (1 800 PICK UPS) or drop it off at a UPS location.

For more detailed information please check out the Flip-flop Brigade FAQ.
It will take approximately 7 to 10 business days from the date your shipment is received for TerraCycle to process your package. Once processing is complete, you will receive your Old Navy coupons by mail.
Download our helpful TerraCycle "Collect, Store and Ship Guide" for tips and tricks that will make the collection process simple and mess-free.
Old Navy is proud of their partnership with TerraCycle and is committed to reducing waste and thinking green.
Flip-Flop Brigade accepted waste: Rubber flip-flops (any brand)