Not really quilting, so I thought I'd better put it under "general Chit-chat".
I've been to Lowe's, Home Depot, Target and Wal-Mart. The only store that sells cotton rope is Wal-Mart and they only have one size. I'm making fabric covered trivets and don't want to use nylon or poly rope - it melts. I want to use natural fibers. As a last ditch effort, I bought some sisal (large twine). That's natural. Thought I was pretty smart until driving home I wondered if my machine will sew through it......sigh. Will let you know.
For those of you who are making the mats and/or bowls, where are you getting your cotton rope?

Did you check online? I use stuff I have had for years.

try Ace Hardware , or a Ranch/ Farm store. I bought mine at Ace. Michaels, or Hobby Lobby might carry it also.

I buy regular cotton clothes line at the dollar store.
I have bought larger cotton ropes in the harware/camping/fishing isle or cording ( fabric isle) at walmart for a larger size rope size

When I used sisal ( fabric covered or uncovered) I placed mine over a inverted bowl ( for shape) and used hot glue to hold everything together.

I bought some hemp rope at Walmart to make trivets. It's like sisal only rougher. I haven't tried it yet but it's not as thick as cotton clothesline so I don't know why it wouldn't work. I do plan to use at least a size 14 denim needle and I can go to a 16 or 18 if necessary.

Try the independent hardware stores like DoItBest, Ace, or TruValue.

I got some at the little family owned independent "DoItBest" type store.

try joanns they used to carry it u could also use apporsty corad in the home decore dpt.

Dollar stores have some cotton clothesline.
I've made a few bowls from what I bought there.
you can check them out at my webshots below

You may try Atwoods, Harbor Freight, or local Ace, etc. I'm with you, would have thought Lowes, Home Depot would have that too.