I had trouble with my John Deere 9170? (don't remember the number, but it was the Deere with the Cummins in it) viscous fan drive.  When I found what they cost, I made some brackets of strap metal to lock out the drive.  I was told that all other JD engines had a lock out kit, except for the Cummins.  Figured if all others could do it, so could I have success.

I had lots of fan belt problems after that, and those flat belts are not easy to change, plus they are expensive.

I finally bit the bullet and bought a new viscous clutch, solved my problems.  I decided the expense of the clutch was much cheaper than all the down time and hot tractor going down when I was really busy at planting time.

Sorry, can't answer your question about a cheaper source, I tried truck repair places, was told that was cheaper, but they couldn't assure me that their clutch would work in an ag situation, and if it didn't work, the problems would be worse than just buying JD's expensive clutch that was designed for that purpose.

Some things are easy to save money on, some you just have to pay the price.

If the tractor engine had a lock-out kit available through JD parts, that would be the best solution.  I was told there would be a little more fuel used without the viscous clutch, and perhaps a bit of a power loss.