As Flareboy said.
It's called an R4.
There are other ones like Acekards.

But. R4s seem trk the best.
They should be fairly easy to find if you just search around online.
I'm sure you could find some on amazon.

There's this azn mall that I go to that use to have this one little suspicious but not sketchy looking vender guy who sold them.
Moderately openly.
I don't know if anyone's still doing that though. Because.
Legality.