Will I be able to get parts for old tractors?

The majority of older brands are still represented by a modern conglomerate even if the brand went out of business long ago. This means that you can still purchase new parts for many of the so-called orphan brands (such as Allis-Chalmers, Oliver, Minneapolis-Moline, Farmall, and Massey-Harris). The trick is in locating who bought out the brand and who to contact. In some cases you may have to follow a trail that goes a few levels (e.g., in 1985 A-C was bought out by Deutz which was bought out by Agco).