Before you create your own listing, you want to ask yourself "why?"
Creating your own listing is the opposite of what we teach because, if you create your own listing, you will need to add pictures, optimize descriptions, and spend time and money to get traffic to your new listing. That is why we always suggest that you list your inventory on existing listings.
If the listing doesn't exist, the product might not sell well on Amazon and you will not have any historical data to research the product.
Sometimes, you might just be having difficulty finding the product so before you write a product off, we'd suggest searching the product on Google since Amazon is usually one of the first search results.