Mercerie Rascol, south of France
https://www.rascol.com/
also,
http://comptoir-phoceen.fr/accueil
Cotton & Color, Switzerland
https://shop.cotton-color.com/en/
An excellent shop on Amazon is "The Quilted Bear" - huge selection, good prices, shipping and service. You can access them from Amazon UK or Amazon France.
Pembertons in Stirling -
http://www.psmc.co.uk/
Sewing Online in UK
https://sewing-online.com/
http://www.barnyarns.co.uk/
http://www.quiltdirect.co.uk/