How could I make dice that always roll the same number every time? (And each side of the dice is unique too)

I manufacture a whip cup and dice which does something similar to what you're asking about.
It's quite unique. The dice seem absolutely normal to a spectator, even if they roll them.

The demo for this is typically done as a game (like yahtzee)... you have 3 rolls to get 4,5,6,X,X. the highest score (X+X) wins.
The spectator tries and cannot score at all. You score every time.

Both use...the same cup and same dice.

Oops. I forgot to mention... the game is played with 5 dice ... also like Yahtzee

Hers are some: http://themagicwarehouse.com/SB5842/Loaded-Dice.html

Here is another set: https://www.mymagic.com/p/mental-magic/7......im-tyler

Jason England has some Casino Gaff Dice, sold in Theory 11 before.
However, the product seems discountined.
https://store.theory11.com/products/gaff-dice-jason-england