I have eventually found what seems to be a wholesale supplier to the florist trade. When I first went to find it, I discovered its hours were very different from normal shopkeepers' times, and it was closed. Today I found it open. But I nearly didn't even get in. I couldn't supply the correct numbers as a business. However, I think that because I couldn't speak the language, the woman gave up and let me go through, giving me the special number after I assured her I only wanted to buy floral tape. Or perhaps it was the pink umbrella and matching rosebud that pursuaded her! There were lots of pink things, many of which I've seen in some of the stores in Düsseldorf. It seems that pink, including pink felt ornaments, and purple will be fashionable this Christmas!