CECILE found pretty vintage ribbons, and hat-making accessories at "Mercerie Utramod", which has been in business since 1890... WOW!
This place is just amazing: buttons galore, embroidery materials, lace, pins and even old rolls of fabrics. "Ultramode" has two shops, at no. 3 and no. 4 Rue de Choiseul, 75002 Paris - tel. +18.104.22.168.45.57, closed Saturday and Sunday (unfortunately they don't have website)