What are some of the toughest mainstream vintage cards to find?

[Kenny Cole]

What is a "mainstream" set? I have trouble considering a card from any set "mainstream" if the set itself is so rare that the chance to own any given card from it is, for all practical purposes, non-existent. For example, I don't consider Leon's T231 Baker to come from a mainstream set because, absent a future find, only a couple of people other than Leon can ever own one.

I would consider the U.S. Caramel Lindstrom to come from a mainstream set because there is a realistic chance to own the remainder of the set if one chooses to go after it. Similarly, all N167s are tough to find, but they can be had if you are willing to write a big check. The total population of almost any particular card from the Cuban issues of the 1910s and 1920s is, for the most part, probably less than 20. However, excluding Pete Hill, Bruce Petway and perhaps a few others, a copy can be had if one looks hard enough. Whether the distribution pattern of Cuban cards is such that they qualify as "mainstream" or are instead "regional" issues, is probably a topic best left for another day.