First, make sure the person you approach has the authority to make the discount you seek, otherwise you are wasting your time.

If they indicate they do have the authority to give discounts, tell that person what you've said in this post - especially that from what you can see on their website, they haven't sold a unit in the past two weeks. When you ask, ask what sort of a discount the person you are talking to is willing to give you.

You may be offered a discount that is less than the full amount you want, but this approach is also more likely to get you something compared to an approach that makes you sound like you think you are entitled to whatever you ask for. After all, they do have what you want and the other stores don't. That is worth something, right?

If you don't like the sound of what they offer, you can take your business elsewhere - except you haven't yet discovered where "elsewhere" might be, yet, and they know it.