Where to buy Soda Ash, Alum and Linen?

I suggest you contact some Quito sellers on Mercado Libre and ask them, who sell tintes para telas and tinte para teñir ropa - ready-made dyes are available.  I don't know where you can find alum and soda ash in raw form (alumbre and ceniza de soda) but the sellers of the dyes might know.

You might also try this search for soda ash:
https://www.google.com/search?ei=5bPUWu … R424mCQmko

And this search for alum:
https://www.google.com/search?ei=l7bUWr … 2OBtSDAuuU

Likewise I would suggest searching Mercado Libre for rollo de tela lino for linen in rolls:
https://www.google.com/search?ei=ArbUWq … 5YamznEXLI

Mercado Libre is a nice source to find and buy hard to find items. But as a seller and buyer, my experience is that some items, like linen, which should be inspected prior to purchase are best bought at brick-and-mortar shops because most of the sellers sell stuff from their homes, or garage and without having a physical store.

soda at mercado iñaquito as bicarbonato de sodio
others dont know((

Sodium bicarbonate does not work in most dyeing recipes, you want instead sodium carbonate (carbonato de sodio).  You can buy sodium carbonate at most swimming pool supply stores - but I don't know of any in Quito.