The wheel mounted weights will be difficult to find. The frame mounted weights not so much.
Many dealers have a weight pile somewhere on site. Wouldn't be surprised if my CNH/Kubota dealer has weights to fit.
Another option is to visit a tractor /implement dealer and ask that they check with North States (do not sell retail) to see if they make weights to fit. Probably do, and they will not cost $200+ each.
Either will make the tractor steer hard without PS or a lifted implement.