Ah... well in that case you have all the pleasure of popping down the Souq when you get here in December.
It's a real treasure trove, and you will have great fun looking for what you seek.
Personally I have never been looking for mirrors, and as a result have no recollection of seeing any there.
One thing to note is that Souq means Market, and there are different Souq's here specialising in different subjects. There is an actual furniture Souq as well, but I think you are referring to Souq Waqif, and mirrors probably won't be that common there.