Old Navy has a great sale today on flannels for adults. I actually love Old Navy flannels and I have a few that I have had for years and still look great.
The regular price is $29 so this is a huge discount but I imagine certain sizes and colors will sell out quickly. You can order to pick up in store, curbside pickup or shipping is free with a $50 order.
One thing I have done in the past if my size or preferred color sells out, is to purchase a different size and exchange later for the correct size once they restock.