Mahindra 2655 HST Cab, Deere 350C Dozer, Case 580CK TLB
I've used strips cut out of a thick rubber truck bed mat before and it worked well. Only lasted a few years out in the weather before it got cracked and would break around the fender washers on the bolts I had holding it on.
Yes, used conveyor belts work very well it just takes time to install them with drilling the holes in the plow to mount the conveyor belt. You also need to have a length of strap iron drilled out to match the holes in the plow to mount them using fine thread hex head bolts, thick fender washers and nylock nuts to mount the lengths of conveyor belt.
If old conveyor belt is unavailable you can always use new round baler belt to do the same job mounting it using strap iron to hold the baler belt in place.
Another option would be slick sheet material from Horn Plastics. They have left over pieces for sale that can be bought in many thicknesses widths and lengths and you can mount them the same way. You will need to cut multiple pieces in longer lengths as a continuous piece will not sag over to act as a snow spray stopper.
The only way that used conveyor belt will work to your advantage is if it is a thin narrow width used conveyor belt as it will have more flex in it to hang down to act as a baffle. New cow stall mats and used thick conveyor belt will not do that for you but if you want a taller moldboard onn your snow plow will work well for you.
Some of the pickup trucks (eg 2008 Ram) had a black plastic spoiler on the tailgate. People like me that bought caps for their trucks had to remove the spoiler. Last year I too saw I needed a upper rubber flap for my UTV 60 inch plow. I realized that this spoiler could bolt right on an was curved good to push snow back down. So drilled a few holes and it fit right on did not even need to cut to length. Worked great last winter. I love it when I find a use for stuff I refuse to throw out (closet hoarder)
Thanks for the ideas, the holes in the plow were there when we bought it through the dealer. Just for the heck of it, Monday I'll call the place we bought the plow from to see how much they charge for the snow guard for the model plow we have.