Aermacchi M.B.-326, Various users

The Aermacchi M.B.-326 is also used nowadays by the American National Test Pilot School. Most of them are ex-Impalas made by the South African Atlas. They are used by the National Test Pilot School located in the Mojave desert, in California.

Regarding the MB-326 in Paraguay, they were bought by the Paraguayan government in the early 1980s from Brazil. They were the Brazilian version, so, technically they were Xavantes. They were involved in many anti-drug operations during the 1990s, like, for instance, when on 6th December 1995 a small number of Xavantes departing from Punta del Este air base, attacked the narcotraffic air force by bombing their hidden camouflaged airfields in the region of Alto Paraná. They served until 2004 when they were replaced by the Embraer Tucano.

Sources:
1. https://en.wikipedia.org/wiki/Aermacchi_MB-326
2. http://www.ntps.edu/component/content/article/49/166
3. http://aeropinakes.com/wordpress/1995/12/06/xavantes-de-la-fuerza-aerea-paraguaya/ (translated)