If it's just roundwire you're looking for, use TEMCo's official amazon store. For cotton get Muji (if you're in NYC, Boston, or Portland, you can get them in Muji retail stores), Labo Puffs, or these slivers. If you want claptons go to wireoptim (not sure if their New Years sale is still live), coilturd or coilclout for fancier stuff like aliens.

I use this personally and it works very well https://www.amazon.com/Japanese-Organic-Cotton-Sliver-Unbleached/dp/B079QH8TLJ/ref=mp_s_a_1_2_sspa?crid=39OEA1JTUDA32&dchild=1&keywords=japanese+organic+cotton&qid=1630896036&sprefix=Japanese+organ&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUE4WjBPRjdRN0dSQUImZW5jcnlwdGVkSWQ9QTAzMTQwOTQyTFpHVlNGT01ZMkVUJmVuY3J5cHRlZEFkSWQ9QTAwNzc2NDgxWk5VWjlVOTA4Szc4JndpZGdldE5hbWU9c3BfcGhvbmVfc2VhcmNoX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=