German Mauser T-Gewehr Anti-Tank Rifle

Seeking an original German Mauser T-Gewehr Anti-Tank Rifle cartridge in 13.2mm (1918). Our museum has an original rifle, and are seeking an original cartridge to accompany the rifle in our exhibit. Because of our exhibit construction, we can display either a live or inert cartridge. Please contact me if anybody can help.

My congratulations to the museum for having a Tankgewehr in its collection.
From a history point of view, I would like to mention that the German army called this caliber 13 mm, never 13.2 mm. As with many firearms cartridges, the actual bullet diameter (indeed 13.2 mm according to Rheinmetall drawing T-Sk-E 2063 of 1934) is larger than the caliber. For example, the U.S. .30 caliber cartridge of WW1 and WW2 in reality has a bullet diameter of .308 inches.
An example of contemporary official German use is “13 mm Tankabwehr-Gewehr” in a Chief of Staff of the Army (Chef des Generalstabes des Feldheeres) pamphlet dated 10th August 1918.
In Germany, following usual army procedure, caliber was not part of cartridge designation. The cartridge was named “Tuf-Patrone” (for example, on a box label of manufacturer Polte from October 1918). “Tuf” stands for “Tank und Flieger” (tank and aircraft), because the cartridge was designed for a machine gun (Tuf-MG) to be used against tanks and aircraft. The rifle was a stopgap.
In a modern context, metric designation of the cartridge is 13 x 92 R (R = rimmed). I am not sure who “invented” the HR (Halbrand, semi-rimmed) addition, so popular today and even found in German literature. The cartridge case has an ordinary rim (2 mm larger diameter than the case). A semi rim would be hardly discernible to the naked eye (.32 ACP and .38 ACP are examples).
I hope the above is of use in avoiding errors in texts accompanying your exhibit.