In Vol XXXI (1841):

Lettre du gén. Pelet; p. 237;
Réponse: p. 347;

Lettre du gén. Pelet: p. 485;
et Lettre du lieut.-col. G. De Illens: p. 491;
Réponse: p. 493.

Note: Starting page only. There may be more pages in each letter/response.

See

Spectateur militaire - Table générale des matières [1826-1878] (1880), pp. 14-15:

http://books.google.com/books?id=LJk8AAAAYAAJ&pg=PA14

I did not realize this was on-line. It is not the same as the one in my collection.