How to find out the suppliers in my niche, without the 'brands' menu?

If there is no 'Brands' menu then it is often a more manual process to find the suppliers within your niche.

The first place I'd start would be to go through the homepage of your direct competitors website. Often they list the brands that they work with on their homepage or they will include a reel of their supplier's logos.

If this is not available then the next step would be to go through their collections. To find this, often you can go to a direct competitor's website and add '/collections' after to their domain in the url bar at the top of your screen.

If neither of these ways are showing you a list of their suppliers, the next method would be the more manual route of checking through their products and listing all brand names that they mention in their product titles.