I've been to many merchant alterers before, and sometimes they say we dont have this material, or that material, or sometimes they have very little of this or that.. well, in my travels, I have never come across a box with a bolt of spidersilk cloth in it, or such...

How about an alterer store, that sells rare gems, rare materials like spidersilk, steelsilk, etc.. would be expensive and you could buy them in various sizes. I.E, enough for a cloak, shirt, or pouch.

Markaela Oraguss, S'kra Mur Warrior Mage