This book contains recipes on the proper tailoring of cultural symbols.
It outlines the need for starting with a rough animal pelt or two crude silk. Fiber filament will be needed to embroider the symbol into the material. It will additionally need water blessed by the deity you wish to attune it to, and crude spinneret fluid or damp marrow as a sacrifice to that deity.
Checked all four merchants on two characters, one with 300 Tailoring and one with 0 Tailoring. The book wasn't sold by any of the merchants for either of the characters.
I found it on the first one I checked in POK. Right under tailored eminent cultural symbols. If it doesn't show make sure your box is not checked to "show only items I can use" and if still not showing then put the word "cultural" in the search at the top of merchant screen and that should pop it up.