How does one find one of those?
Go to your bishopric’s website and usually you’ll find them listed under ‘excommunicated’ or ‘schism’.
Many Sedevacantist churches and chapels make their principal mass of the day available live on the internet. They can be found by googleing ‘Latin Mass’, or ‘Traditional Roman Catholic Mass’. Worshippers who don’t have a traditional Church available in their area can follow along with their missals and be rewarded instead of feeling condemned by the new religion.