@djwdjw OH NO! Your dog was either hungry or found a new toy!
Unfortunately, we don't sell REI Co-op Saddles. We only have one kind of kid's saddle on our website. Bontrager Comfort Bike Saddle - Kids'
You may also want to contact your local REI bike shop, as they may have some bike parts available that are not shown on our website. No guarantee that they may have the exact saddle you need but they may have other ideas on how to find one.
Best of luck! I hope your kiddo is able to get back to riding asap!