Your front hubs (and whole front suspension) looks like it was from a 2-WD quad.
You could start by
accurately measuring what 3-bolt pattern you have, (measure it in millimeters) and then compare your measurements against the specifications you'll find
at this link:-->
http://www.mud-throwers.com/atv_wheel_chart
Then after you learn what brand/model rims match your measurements, you'll have an Idea of what brand/model of quad rims you need, and what front hubs that
might fit your kart spindles. Then if you found that hub for sale somewhere, you could accurately measure your spindle diamiter/length with a caliper (again in metric) to confirm that new hubs mounting dimensions/bearings will correctly fit your spindles diamiter and length.
Then, you'd probably need to contact the hubs seller, and ask them to measure their hubs dimensions, so you could compare that to your spindles making 100% sure everything will fit...