OK, I found a newer one:

Application form for the first year fee-free Delta Gold AmEx card with 10,000 bonus SkyMiles: bottom left corner of the form: FF7 T01AD01219, bottom right corner: D2FY OPGTA. Number to call: 1-800-482-9500.

I also called that number and inquired if that application is still valid, and was told "yes".