There are no 'rules' when something like this happens as the situation can vary. It will have to be worked out between you and the seller Where is the seller located? If they are overseas or even in the U.S., it is unlikely that they would pay to expedite the order as it would probably be very expensive. If they are in Canada, you could ask if they would be willing to send it xpresspost but they aren't under obligation to do so.
Does the seller only have one of the item and that's why they have to wait to send it to you? Or, could it just be a stalling tactic?
I think that the fastest solution would be to ask for a refund and try to find something similar from someone else.