You can try contacting Merchandise Guest Services, but my guess is the shipping would be cost prohibitive.
Merchandise Guest Services: 1-877-560-6477
Email Address: Merchandise.Guest.Services@DisneyParks.com
Otherwise, you might want to try the resale market (e.g., eBay or Amazon.com) or look into personal shoppers (again, the shipping and handling might be cost prohibitive).
Although, I agree, the "best" option is go back to DLR and get another one!
Or ask someone to pick one up and mail it to you. People do it with maps all the time but maybe you'd just offer to pre-pay so they know you're good for the cost of the decal + postage.
You can try contacting Merchandise Guest Services, but my guess is the shipping would be cost prohibitive.
Merchandise Guest Services: 1-877-560-6477
Email Address: Merchandise.Guest.Services@DisneyParks.com
Just thought I'd report back @figment_jii that I got a response from the email you provided. They included a pic of the decal to make sure it was the right one and gave me the item # so I can order a replacement. Pretty cool since they could have just said nope, it's only available in the park!