There is no sure-fire way to find and purchase any type of discontinued cosmetics. The safest way to purchase discontinued lipstick is to use a company that will make a custom blend to match your preferred choice. It will not be from the same brand or in the same packaging, but the color should match exactly.
Brands do not keep discontinued items; once a store sells out, the product is gone for good. There is no way to tell if discontinued items found online have been tampered with, and there is no way to guarantee their quality.
There are many options when searching for a company to match discontinued cosmetics. There are many reputable online sites that will match your lipstick, and this may be the most viable option because it is much easier to find these companies online. One drawback is that many of these companies require you to send them the discontinued product in order to match the product. There are also boutique stores that specialize in mixing cosmetics; however, it can be more difficult to find one of these as locations are limited. Bring in the discontinued product, and an expert should be able to mix a new product in order to match the color of your product without you having to relinquish your original sample.