Given the same sources provide such information for vehicles that clearly have optical systems, the lack of any discussion indicates the lack of a system
Following your advice I have checked again my books and you were right. The
"Gli autoveicoli da combattimento dell'Essercito Italiano" vol. I (p. 558) describing different versions of L3 under
"Apparati ottici" leaves blank spot for L3-33 and L3-35 giving some details for optic equipments only for L3-38.
Also Pignato & Cappellano provide a bit different ammo load :
L3-33: Fiat AV - 3800 rounds (76 x 50)
L3-35: 2 x Fiat 14/35 - 2320 (29 x 80), however in special cases it could receive supplementary load of 800 rounds which give us additional 10 reels, bringing it up to those 39 reels referred to by your source, Jeff (p. 536)
L3-38: Bredda 38 - 2400 (100 x 24)
Best regards
Slavomir
P.S. Cappellano & Battistelli in
"Italian light tanks" for L3-35 give 2170 rounds in total.