This set is one of the few vintage menko baseball sets that is easier to find in the United States than it is in Japan. Back in the 1960s Americans Bud Ackerman and Mel Bailey imported a lot of Japanese cards to the US and this set was among them. You can read about it more on Dave's excellent post about the history here.
So in the US its quite a bit easier to find than other menko sets. In Japan in contrast its not really noticeably easier or harder to find than most other sets from the same era.
This sheet never left Japan. The ones that were imported to the US (by Buck Ackerman with this set) had numbers stamped on the backs. This one doesn't have any numbers stamped on it which, along with the fact that I bought it in Japan, means it wasn't among those exported:
Another point of interest about the backs of this one is that it is printed in green ink. According to Engel this set is most commonly found with brown ink backs, while green ink backs are rarer. I'm a bit curious if all of the exported ones were brown ink backs, while the green ink backs like this were never exported, which might explain why they are rarer.
This sheet is missing the key card from this set - Sadaharu Oh - but it has two of the other big names. Isao Harimoto, Japan's all time hits leader and all around amazing guy, is on the lower right card while Katsuya Nomura, #2 on NPB's career home run list is on the top right one.