19" on the Drop Top When I ordered my 335i Convertible last year, they actually had a coupe in the showroom with the 19" on it. I ordered mine just like that but the dealer did inform me that it would not come from the factory like that and that they would have to do this at the dealer. I took delivery of the car with the 19"ers mounted and took the 18"ers home for spares.
ripster I ordered mine in mid-February. The car was ready in April but I took PCD delivery in May. I would try to push for getting the 19"s as you take delivery, as mentioned by hbosch. Unless you live somewhere warm, it'd be ideal to have a different set of wheels that you can mount all-season / snow tires on. Good luck!