Charging cradle contacts for transponder cradle

I have a Mylaps AMB Classic Kart Transponder (TranX3 160) and I want to make a 3D printed cradle mount for installing in my trailer.
Any ideas where I can get the charging contacts for the cradle?
I see other people are 3D printing charging cradles, I just don’t know where the charging contacts come from.
https://www.ioportracing.com//images/products/transponder-charger.jpg