My two fit in the one we have with lots of room to spare, so I believe if you're looking for one for two Yorkies, most regular sized strollers would work.
The one we have is like this ---- although in blue of course! I don't think I paid quite that much for it (maybe I did) and don't remember where I ordered it. I did order it online and remember doing a bit of searching to find one with the features I wanted at a decent price.
http://justpetstrollers.com/happy_tr..._stroller.html