1988 John Deere 750, 1938 McCormick-Deering (Farmall) F14
Depends. What make/year of tractor? There's a bunch of folks out there that have "restored" guages in stock for early stuff (roughly pre-1960). They may have what you need at a fairly reasonable price.
Some folks do their own, the trick is getting the bezel and face glass off without screwing it up. Again, depending on the make and year, replacement glass and bezels may be available.