If a piece of equipment is expensive enough, someone will occupy the niche of fixing it so the equipment owner doesn't need to replace it immediately. For example, one of our family businesses is repairing electronic components of industrial equiprment, which often involves hunting down spare parts in Asia.
HOWEVER, most niche businesses of this sort are too small to deal with the bureaucratic hurdles presented to vendors by government entities or companies as large as Amtrak. Taking our example again, our customers are mostly smallish to medium-sized machine shops. Really large manufacturers have either in-house staff keeping older machines going, and/or newer machines.
So it's possible that Amtrak doesn't have any good options for repairing things for which spare parts are no longer provided by the things' manufacturer. I doubt Amtrak has a crack team who can improvise repairs like this.