See, they found you. It’s a good thing you saw them too, before they attacked you!
If I was you it sounds like you need a 1” fully keyed axle. 34” - 36” long with a sprocket mount, rotor mount, bearings and keyed ATV hubs.
You don’t find axles. They find you!
Seriously though have you tried Amazon, Azusa, BMI, GoKart Supply, Go Power Sports, MFG Supply? You have to build to suit you.
That kart looks like a home build and not a factory built kart. BMI, GoKart Supply, MFG Supply, Azusa, Amazon, Go Powersports and a ton of other places are going to be your best bet for parts. And get rid of those Harbor Freight hand truck tires!