As far as I checked briefly, there is no Gyokai-Dantais for cycling wear. Usually Gyokai-Dantais are according to the category of distributional channel. I believe that the major distribution channels for cycling wear are sport goods shops as well as bicycle shops.
Brief searching in internet shows me the existences of Gyokai-Dantai of the following fields.
1. Sport Goods Manufacturers & Distributors
2. Bicycle Manufacturers & Distributors
3. Cycling (Leisure) Facilitators
4. Apparel Product Manufacturers & Distributors
I assume that some of the member lists of the category #1 to #3 would meet your demand. There are several major Gyokai-Dantais for the category #4 but I suspect the priority is low from your view point. You can find them in the internet simply by typing, for example, “Jitensha Dantai” into Google. (You have to type it in the Japanese language, though.)
I hope this information will help you.
I am glad to hear that my info inspired you.
To deal with Gyokai-Dantais and to utilize their abundant information sometimes require specific approaches. And some of them are conservative enough to be incooperative to outsiders.
So if you face the difficulties in dealing with them after you contact a few Gyokai-Dantai, please let me know. I can probably give you brief advice.
And if you had specific problems in expanding your business, my service could offer you good solutions, as I do for my regular clients.