Title. Not sure if this is an oversight or what, but after buying the Cayde's Duds shader for bright dust from Tess, it appears at the top of my collections list for shaders under "Seasons", but cannot be bought back. Hovering over it has a red banner saying that it is an "exclusive item", and there is no option to reacquire.
Same thing goes for the Queen of Hearts ship from the other week - it's in my ships tab, but can't be reacquired.
So, take care when clearing out "eververse" gear not to remove the exclusive Cayde items, or you might not have a way of getting them back!