Apparently some received theirs a few days after, as they claim that you should receive it shortly after device arrives.
In my case it did turn up with the device, but god knows where i lost mine.
I did get an email regarding Trade-In Reminder from Samsung.
Bottom of that email it stated the following. (See Attached)
I just got the return labels via email, printed 'em off and stuck 'em on my return package.
Hope it helps.