Your question about buying low-production stamps suggests that you're looking to acquire them as an investment. If this is your intention, I would advise against it.
The Famous American series, like most stamps of that era, were hoarded in mint condition, so there is a glut of them now. Even nice stamps from the 1800s are tough to sell for more than 15 percent of catalog value, in my experience. Mint US stamps from the 1930s to 1940s are even harder to sell, and judging from trends in the number of people collecting stamps, demand for them likely won't increase in the future.
Some areas of US philately are thriving, but I don't get the impression that US stamps from the 1930s to 1940s stamps are one of them.
Here is an article that may be of interest:https://www.nytimes.com/2017/09/29/...ilately.html