To help make life easier, Costco97, a blog dedicated to the wholesaler, created a toilet paper tracker. It allows you to go online and check the stock of your local Costco before leaving your home. The site also tracks the availability of paper towels, disinfecting wipes, water, rice, and Lysol.
The tracker does not list the exact number of items in stock, so the best way to ensure they will still have the items is to check before they open and try to get to the store as early as possible.
If you are running low on toilet paper, there's an online tool that will help you calculate how much longer your supply will last.