No, it's not the same. Quite.
The original branch associations were formed in the late c.19th by "associations" of individual officers. Cavalry naturally was first, but the Infantry Society eventually came along in 1893 (remaned the Infantry Association in 1921). The branch associations published their journals for their members, but copies have been reasonably well preserved at the school libraries, as jgawne suggests.
Leavenworth is especially good for the early years, as it was both the Cavalry and Infantry school then; but poor security in the library in past years has resulted in the removal of a lot of important material by transient students. Yes: some officers are thieves.
After WWII, a number of the associations merged to join the Association of the U.S. Army. The Infantry Association was one of these.
In the early 1970s, DoD prohibited the staffing of the professional accociations with active duty personnel. Some were able to continue independently, like the Armor Association; some folded. The remaining branch journals were continued by the respective schools and centers as official army professional bulletins.
These now include Infantry Magazine, Armor magazine, the Field Artillery Journal, Military Intelligence magazine, and others. They are usually produced by some element of their respective schools; for example, Infantry magazine is produced by the Directorate of Operations and Training (G-3) at Fort Benning. The remaining branch associations usually purchase subscriptions to the bulletins for their members: a weird sort of symbiosis.
Regarding Infantry, specifically: in 1982, the Infantry Association was reestablished at Fort Benning; its members recieved copies of Infantry magazine. In 1994, it was restructured and incorporated as the National Infantryman's Association (a non-profit), and in 1998, was renamed as the National Infantry Association. Since 1999, it has published a second periodical, the Infantry Bugler, as a newsmagazine for its members.
So there is some continuity, although the proponency for the branch journals has transferred from the branch associations to become official publications. And the branch associations themselves have changed considerably in the last 123 years, since the U.S. Cavalry Association was formed.
If you're looking for a specidic article from the Infantry Journal, and can identify the author, title, and issue, a letter requesting a copy to:
U.S. Army Infantry School
6751 Constitution Loop
Attn: Donovan Research Library
Infantry Hall, STE 101
Fort Benning, GA 31905
USA
might get a positive response.
Allen (who used to publish an Army professional bulletin)