How we can get this Amulet, because I want to collect unique item
Finish all Thieves Guild quest (?)
Yes like the wiki page says finish the the Thieves Guild questline (Under New Management is the very last quest), but if your on PC and really want it you could spawn it with console commands instead.
Is there anyway I can get the real thing, like actually wear the amulet in the real world.
You mean, like mershandizing?
Etsy sells stuff like that and if they don't have it contact one of the Jewelers who used to make them ( I know I have seen it on the sight, at one point EVERY amulet from Skyrim was/is on there).
What do you think?