There are people out there that will strip down and recondition starter motors- could be an option if you cant source a new one.
In the mean time, take it off yourself if you are up to it, and just clean every thing you can see, blow it out with an air line, give it a tap with a hammer as mentioned above....youve nothing to lose put it back together and give it a try. Check all the big cables that supply it, and make sure battery connections are tight, slacken them, twist them a bit to ensure contact then tighten again.
If all else fails you should be able to tow start it, (tricky if there is snow lying as you need grip for the wheels, prepare it as if you were going to start it normally, stop in, ignition on if it has one, Select the highest gear (ie road going gear) , tie to the back of your truck and once up to speed let out the clutch steadily, all being well youll be in business.
As an aside, diesel can freeze but it doesnt appear to be the problem you have here, The sign that your engine is getting fuel is to turn it over on the starter...if fuel is getting through you will see white smoke coming from the exhaust, if it isnt fuel isnt getting through could be frozen diesel, blocked filters or no fuel in it !
Diesel in its standard form will freeze the process starts at around 0 deg C. So why arent all the cars on the road stuck at this time of year ? Well firms put in additives during the winter so when you buy disel at the pumps it wont freeze. Probelm comes if you fill your tank in summer and dont use the vehicle much, winter arrives and it still has summer disel in. Farmers of course usually have a big tank, if they fill up with winter diesel whilst the tank is still say a third full of summer diesel you end up with something in between.
At the moment in this extreme wether, i have a little 1 Kw fan heater in my shed, about 10 mins before starting the tractor i set it off as close as i can pointing at the side of the engine where the fuel pipes enter the injectors, This warms the fuel in the pipes and the injectors slightly and i find the tractor starts instantly as though it were summer saving a whole load of strain on the battery, Only any good of your tractor is under cover and you have an electric supply i guess.