I can’t say for certain yet (as I haven’t collected more than fifty of one item of junk yet), but it would be odd for there to be a different max number of items for consumables and junk, so I would strongly suspect that the cap for an individual piece of junk is also at least 200.

I can say for certain that you can’t have more than 50 unique items, and that if you try to collect a delivery that would give you 51 unique items, you get a message saying you have too many items, but you don’t lose the delivery. Once you sell all of one item, you can accept the delivery without a problem.

I’ll resume stockpiling junk to see if I can break 50 of some junk item.