I don't think there are any exact numbers...if I recall, there is a "Caldera Ledger" or two which simply say ("The Ledger contains information regarding shipments of ebony, everything seems to be in order")
I would say your guess is as good as anyone's. While the Imperial takeover of the Caldera mine seems fairly recent, it may have been mined before then by Dunmer, although since the whole town has an Imperial feel, perhaps it has not been fully exploited until fairly recently. In that case I would guess that production would be fairly high compared with older, exhausted mines. Now, exactly how many pieces of ebony is that? 5 a day? 10 a day? I couldn't say. I wouldn't put it too much above 10 just because ebony is such a rare, precious resource. I would even say that it could be as low as 1 a day and up at as much as 5, but not much more. IF you run willy nilly and grab as much as you can, you might get 10 pieces, but who knows. In that case I would say that shipments would go out every week? Seems like a good, regular schedule to me, and if the average daily share is 2.5 pieces, that would be something like 15-18 pieces a week, and if I remember correctly they are (market value) 500 gold, so 6,500-8,000? I'm really not even crunching these numbers too accurately.
I don't know what you need this for, if you're planning a mod or are just curious. For some reason I actually happen to be fascinated by all the minutiae which seem to go around Morrowind, like the mines, the farmers, the fishers. It's something that I thought was lacking in Oblivion, and although not fleshed out completely in Morrowind, it did provide a backdrop, and the ability to add mods easily, like the "Skooma Drug Lord" mod.