In Season 10 Episode 5 of Supernatural, Marie ends up giving Dean back his amulet.
How did she know it was the real thing?
If you look carefully during the production, the Dean character of the Supernatural play is wearing a replica of the Samulet during the production.
Marie, once she realizes who Sam and Dean are offered it to him thinking he needed a reminder of better and worse days.
A replica Samulet appears in the musical in 10.05 Fan Fiction. After Marie says Dean should never have thrown it away, he states he doesn't need it to remind him how he feels about Sam. however at the end of the case, when she gives it to him, he keeps it and hangs it from the Impala's rearview mirror. Supernatural Wiki: Samulet
You did not look closely enough. After she gives Dean the amulet, it cuts to the end of the play and you can clearly see the girl playing Dean wearing the prop amulet. Looks to me like Dean got the real one back.
It actually isn't the real "Samulet." if you remember, the original was made of a bronze like material and was much smaller. At the end, right before the bringing back of the use of "Jerk. Bitch" between Marie and Dean, she gives him a copy of the Samulet. However, it is much bigger and made of wood that is just painted gold. There may have been some confusion because after Dean receives the fake Samulet, the actress playing him is seen wearing it. This could mean one of 2 things. First, the writers just over looked that. Second, many people know that if you have ever been in a production, they sometimes have an extra copy of a prop, especially something small like a necklace. So in short, Dean received a fake Samulet, and his actress counterpart also had a copy of it. So unless you believe the headcanon that Sam picked the real Samulet out of the trash can 5 some odd years ago, the chances of us ever seeing the God-finding necklace again for real are almost nothing. If you need more clarification, just look up "Samulet vs Fanfiction Samulet." You should get a good look at the difference.