I think AGCO has the screens.  They may be a little pricey, but if you elect to use it without one and the tractor gets hot because of stuff in the radiator you might decide they were not  that expensive after all.

When you bought the tractor and the owner said it was "overhauled" did he tell you what they had done?  It is hard to imagine the bearings are bad now if they really did an overhaul.