There are few records I have been able to find on production of the original Mle 1866 Chassepot cavalry carbines. However, Royal Tiger / InterOrdnance just recently brought in a crate of 200 Gras and Chassepot-Gras cavalry carbines and I was able to help unpack and sort them. In the process, I found examples of all three main types of markings.
The pattern was adopted in 1869, and production began in 1870. The first roughly 55,000 at St Etienne were made under the Second Empire, and marked “Manufacture Imperiale”. Following the defeat of Napoleon III and the fall of the Empire, the marking changed to just “St Etienne” in large script letters. About 100,000 cavalry carbines were made with this marking, in 1871 and 1872. Finally, after the Third Republic was formed in 1873, a final 25,000 or so were made with the receiver marking “Manufacture d’Armes”.
The examples were are looking at today were all converted into metallic-cartridge Gras carbines in the late 1870s, as were the vast majority of Chassepot carbines – originals still firing paper cartridges are extremely rare today.