Back in the good old days you could get custom units from EMD, GE and perhaps one or two other builders depending on the time frame who had experience, a track record, and more or less knew what they are doing. I'm not sure who would fall into that category today, either by choice (don't want custom job shop business) or skill level. And even if you could, the quest for fuel efficiency and low emissions has apparently made new locomotives much less reliable than the old simple stuff. It will be interesting how the new units on the White Pass turn out when they are put to the test.
JBWX