I can't seem to find any information (in-game or online) about the capacity of the supply convoy, and I'm accumulating a lot of equipment that might not get used up anytime soon.
I have played a lot of different games, but I have only played Fire Emblem Awakening, Fates: Birthright, Fates: Conquest, Fates: Revelations, and Echoes, but while there are definitely caps in many games, I haven’t found one in Awakening yet. At least in terms of inventory. Max gold is 999,999. Max level is either 20 or 30 depending on what class the character is. My convoy is 277 in swords, 258 in lances, 242 in axes, 250 in bows, 339 in tomes, 89 in staves, 29 in stones, and 381 in items. That’s 1,865 in total. I didn’t even include the items that had any uses on them or were equipped to a character. I don’t think it’ll be easy to cap your convoy. Now excuse me while I restock my convoy with more items.