First, have you added wheel weights and added ballast to the tires themselves? This can make a big difference in traction. Ag tires do give more traction but they tear hell out of the ground.
The dealers here carry different tires/rim combinations for your tractor, but it won't be cheap.
industrial tires are a nice in between choice also ,I would try wheel weights first before using fluid in the tires.But if fluid is used I think tractor supply has the fill kit reasonable.use non corrosive,non freezing fluid in them,here the county coop can fill them.
We should have rear R-1 Ag tires and rims in stock, I will make you a special deal on.Let me see what I have and I will let you know, I responded to your e-mail also