Traded to the Cardinals in 1950, he was soon sent to Houston, the Cards' AA team, then was promoted to Rochester, their AAA team for 1951.
The Baseball Reference page ends his transactions there, with the Cardinals trade. But in 1952, he was sent to independent (at the time) Syracuse. From the Pittsburgh Post-Gazette of May 23, 1952:
“John Blatnik, outfielder with Rochester, has been sold to Syracuse, also in the International League”
Syracuse came under the wing of the Yankees in 1953, and then the Phillies in 1954, so Blatnik was back in the Phillies organization when he was sold to Buffalo for 1956:
“Bison President Reginald B. Taylor closed the deal and also announced acquisition of infielder Lou Ortiz and outfielder Johnny Blatnik, both well known in International League circles. They were purchased through the Philadelphia National League club farm chain with Gene Martin, formerly at Syracuse, representing the Phillies”
This article, from the Buffalo Courier-Express of Friday, Dec. 2, 1955, talked about those deals and the Bisons hiring Phil Cavaretta to manage.
Blatnik's career ended with a few at-bats with Buffalo that season.