Glad that Chris beat me to it, as there is no difference in what you orderand how soon you will get it, based on a Coupe or a Convertible. Will there be delays if you want a specific color, or currently the two-tone interiors , for instance,sure.
A Dealer , regardless of size, can not tell you he will get a convertible next Spring, as no one has their allocations for that far in advance.
Hate to say this, as it is another one in our profession, but this is a very inappropriate bluff, and I would simply ask him how many cars he is getting this month ( he should know next week ) and can he get one for you.
Best of Luck!