Luck... a human-made fanciful concept thought to implicate positive events. Well, I don't believe in luck. Events just occur, and it's not that if I have some kind of strange shiny object in my pocket, they would've differed in any way. Objects can't determine the future; lucky stuff is just there to give you more hope and confidence, yet it doesn't
technically work.
Same idea applies to the opposite theory: unluck. Come on, if I walk under a ladder, shatter a mirror or a black cat passes me by (which happened 10000 of times), I'll have unluck? That's hard to believe I'd say.
Long ago, I used to believe "7" was my number of luck, but actually it didn't bring anything positive in my life.
So let's summarize my answers to these questions:
Does that thing gives you luck when needed?
Number 7? No, not at all.
The same they would have been without believing that number 7 would have brought me luck.
and most importantly is where I can get one?
Any magic shop in your city that sells talismans and amulets, or simply visit tarots and buy their crap. (ok, I was just kidding XD)
You don't really
get one. You...
baptize an object as lucky, probably because you think it brought you good fortune in certain situations, or just because you feel it from inside and can't explain it.