I've been looking around myself, and we've been able to inspect resource locations using tools and it looks like there are currently zero T10 clay nodes in the game. If T4 mushrooms are on the agenda to resolve, this should be fixed before the first settlements start needing this resource.
#T10 Clay is not spawning
restive cairn
weary veldt
t10 clay is only needed after people get 100 foraging pushing a t9 claim past 9 doesnt even use t10 materials so safe to say its not happening for awhile. While i agree it needs addressed, they should have the tools by now to remedy missing resources id think, they plopped in giant dungeon structures.
gloomy agate
-# tbf building a building 27 times is a lot easier than fixing whatever constraints the resource agent has that doesnt allow them to just add a resource id to a list and have them magically start appearing correctly