It is very likely that Germany did have “submarine contacts” with Argentina in early 1945 ( even during the whole war). Many high ranking Nazis were plkanning their “bolt-hole” in case of disaster ( which many did use fromlate 1945 to the early 1950s;as to the MP/Stg44s and ammo, also very likely. The Argentine Army at the time (late 30s, early 1940s, was, Image wise, the mirror of the Wehrmacht ( uniforms, Firearms design, Tactics, etc.)
The Argentine Ordnance organisation began making a prototype of the MP44 design very early after the war — samples (finished) and blanked out steel stampings are in a special display at the Museo de La Nacion. Plaza San Martin, Buenos Aires.
Large quantities of Ammo (7,9x33) was also made for tests etc. But changes in Latin American Politics (heavy influence of the USA) led to Argentina adopting the 7,62 Nato calibre FN-FAL in the early 1950s, after trying out a 7,65mm calibre FN 49 Semi- Auto for several years.