Apache Yakyugun (known in English as Apache Baseball Academy) was one of Toei Animation's earliest anime, adapted from a manga that ran in the now-defunct Weekly Shonen King. It ran for 26 episodes from October 6, 1971, to March 29, 1972.
As of the time of writing, only three raw Japanese episodes have managed to find their way online, and no English subtitled version is known to exist, though there have been references to an old VHS fansub possibly floating around the market.
There was a complete box set released in Japan. However, it had a very limited print run, to the point where eBay listings go for thousands of dollars in American currency.