These yarn brands have been discontinued. Are they no longer made, or is there any stock available? You can still read about the yarns to refresh yourself on what they were.
Sisu Discontinued Colours - Art of Yarn
Discontinued (?) yarn mid project (Australia) : r/YarnAddicts
Looking for discontinued yarn : r/knitting
Knitting yarn - arts & crafts - by owner - sale - craigslist
Cascade Yarns Lana D'oro, Superfine Alpaca and Wool, Light Worsted Weight, Rare Discontinued Yarn - Canada
Find Discontinued Yarn Group
Discontinued Yarn, or Why I've Added to My Stash Recently – Threadpanda
Substituting Discontinued Yarn
Discontinued Yarn, Yarn Bee Yarn Debut in Stormy Blue Color, Yarn Bee Debut in Blue Color - Canada